Ok, you need much more infos then.
Trade :
First, do NOT check the tooltips about trade, they are always wrong and useless. Instead, try and see how it goes. Move a merchant somewhere and see if you make more next month. Collect somewhere instead of steering and see if you make more. The more you play, the better you will be at guessing this without having to try.
There are several things that are always true however. If a coastal tradenode goes in only one direction, this is useless to have a merchant in there if he can be somewhere else, because you will automatically steer trade and a merchant will only give you +2TP. In an inland tradenode like Champagne this is worth it because you get around 50TP from the "caravan". If a tradenode steers in different directions, like Ivory Coast, you have to have a merchant there. The tooltips are bugged. They say something like "steering 10 ducats towards Sevilla" while it is actually steering an equal number of ducats towards every reachable node unless you have a merchant to direct trade, so 2.50 towars English Channel, Bordeaux, Caribbean and Sevilla in such a situation. However, if you have a merchant steering in Safi, he is useless since the difference is the difference between 4 ducats and 3.9 ducats steered towards Sevilla. Am I being clear?
However, this can obviously be worth it to collect in a tradenode like Safi. This depends on your number of merchants, your tradepower in Sevilla and in every other tradenode where you have a significant power, and the ratio between your TP in Sevilla and the total TP in Sevilla. You can theorycraft it by using a formula, or just try, as I said. This takes only 2 months for everything to be set up and you can see if there is any significant difference. I don't know if you are familiar with the basic concept behind collecting out of your homenode: you get -50% tradepower there, which is a big deal if this is a big node where you had 40% or something, but is insignificant if this is a smaller node where you had 90%. You also lose the transfer bonus in Sevilla, and this can be very meaningful. If you have a lot of merchants steering trade all around the map in a global trade empire, you can have over +100% in your homenode, this is insanely strong to monopolize it without attacking Spain. You renounce all of this by collecting in Safi.
The basic idea is usually to abandon the idea of steering completely once you start collecting elsewhere, because the transfer bonus is lost anyway. So if you collect in Safi, collect in every valuable tradenode. There are a few exceptions to this, if you can get some "almost endnodes" like Zanzibar/The Cape with a very high tradepower, you could have a strategy where you steer trade from everywhere in Asia towards them, collect there, and collect in Sevilla as well to have the American money. This is optimal if you have 0 control over the Ivory Coast, but this is not your situation at all. Worth mentioning though.
In a nutshell, 90% of the time this is best to either steer everywhere towards your homenode, or collect everywhere around the globe, but not do a little bit of both. In your situation, you have a low control of Sevilla and probably a high control of Safi, so right now this is probably better to collect in Safi, but in the long term this is probably better to steer everything towards Sevilla to get as much control of the node as possible thanks to the transfer bonus, and to make it the most valuable tradenode of the game. This is even more important in 1.18 because this guarantees the fact you spawn Global Trade.
Navy/Economy:
You have far too many heavies right now imo. Heavy ships are extremely expensive and not that useful in an early SP game. Especially if you are allied with Spain, they can provide a lot of heavies themselves. Just check the war screen there. Your side has 23 heavies, their side has 3 heavies. DO not sink your heavies, but leave them mothballed. They are a budget hole early game, and having a good budget early game is so important because your early benefit gets snowballed over the game. Having more money very early game means more lightships and more churches and workshops, so more money at lvl 11, so more manufactories, so even more money lategame. This is why this is usually better to have 0 heavy and 0 fort very early game. It's not that they are useless, it's just that not having them early allows you to have more of them lategame.
You say you use your heavies to protect yourself against pirates. You can use lightships for this as well. This is poorly explained but they will give you tradepower as well when they protect you against pirates. And maintaining a huge fleet of heavies costs more than what the pirates take away from you, usually. Overall, you should have a much bigger tradefleet imo. Here this is better to do the math, because you can't build the ships and destroy them later without a huge cost, so you better be sure before building them. So here is the idea. Early game, a tradeship costs 0.04 per month and costs 20 ducats. It makes money if the 2TP it gives you in the node it collects in allow you to have more than 0.04 ducats more per month. I would need a screenshot of Sevilla to explain it to you with precise numbers, but this should be super worth it to protect trade there. If you win 0.06 ducats per month per light ship, then the lightsip is as good as a church that would give you 0.10 per month, which is considered the base from which you should build them in a normal situation. Light ships are overall the same, they are useful in wars as well, but they can be destroyed, but they can also capture ships, so overall this is about the same thing. Early game, before you have a lot of heavies, simply mothball your tradefleet if it is in a dangerous war. This one is not dangerous because your side has an overwhelming naval supremacy. If you win 0.08 ducats per month per light ship, then the lightsip is as good as a church that would give you 0.20 per month, which is massive. This is possible that your ships would grant you even more, I would need a screenshot of the Sevilla tradenode to do the calculation.
You are allied with Spain, this means you have a huge meatshield, but also means that noone will want your land because no ennemy neighbours you. This is why Portugal is considered the best country for beginners, you cannot lose land of the entire game if you are friendly with Spain. Even if you are fully occupied they will only ask money, and breaking alliance with Spain. This means you should not be affraid of losing a war, and should not overcommit in them. Protect Spain if they are your ally because you don't want France to invade them totally and destroy them, but abandon your country or separate peace if you are losing the war, there is no problem in that because you will only lose money, and that would cost you more money to fight the war. That's also why you should not have forts imo, they are taking a lot of money from you for nothing right now because all the fighting happens in Spain. The best way to have a massive economy lategame is to reduce the costs to a minimum early game. Your budget should not be balanced. It should be heavily in benefit, so that you can build buildings to have even more money later and so on. This money is used to run several colonies at a time, to spam mercs and conscription centers. This way, even Portugal can match France from midgame, and you can have one of the higher forcelimits lategame. If you use forts and heavies early, there is no chance you can do this.
Diplomacy :
I guess France rivalled you. That's sad because that's too late to turn things around and betray Spain. But you say your France isn't impressive. It did not blob, but it is a lot stronger that Spain, or that any country in the world actually, except maybe the Ottos. Heck, you are allied with Spain and you seem to say that France wins. Imagine if you were on France's side... Here you condemned yourself to never having a full control of Sevilla. If you play another Portuguese game and do the opposite, ally France and kick Spain, you have a full control of Sevilla for free so your ships can do something else and you make a lot more money. Spain has no PU on Naples either, so they are weak and they will never expand because they neighbor only France and you. They will eventually be more of a problem that an helping hand. That gives some challenge though. Try allying Austria then, especially if they kept the emperorship, they will protect you and they usually don't do suicide offensive wars in which they call you. Spain is usually a pretty weak ally lategame but I guess you have no choice but keeping it now.
Wars :
Always be on time with military techs. This should not be hard because you are a western country and military points are not really useful for anything but teching. There are ideas of course, just be careful not to dump every points in them instead of teching, techs are better that ideas usually. Only develop if you have no tech and no idea to take.
What is the composition of your stacks, and which military tech are you at?
The optimal stack is something like 12-4 before level 7, 12-4-4, 12-4-6 or 12-4-8 after cannons depending on your income, but usually 12-4-4/6 early and 12-4-6/8 after level 13, when artillery becomes a thing. If you have money issues, be at a minimum number of 2 art pre13. I usually go with 16-4-10 around level 18 with the increased combat width but this depend on your income. You slowly increase artillery and reduce cavalry after that to end up with something like 20-4-20 lategame, or even 20-0-20 depending on point of views. Level 22 is the real turning point for artillery from which it becomes insanely good and level 25 is even more good. The idea is that you should have a full combat width made of infantry and some cav to flank, and gradually have a full backrow of artillery, ideally a full backrow of artillery from level 22 or 25. This is always good to have more artillery if you can afford it, it's just that artillery is not that good pre-13 and very expensive. It is OK between 13 and 22, strong post 22 and godlike post 25. Artillery can fire from the backrow as you may know but it takes heavy casualties when fighting in the frontrow. The lategame strat is to have the maximum number of artillery, and to protect them as much as you can with mostly infantry in the frontrow.
Apart from that, consolidate your stacks before every battle. Shift consolidate allows you to consolidate without losing regiments. This is more expensive in the short term and less expensive in the long term. Always have a general leading your army. Be careful with terrain. Engage with one stack and reinforce the battle gradually with the other stacks, because if you engage with 4 stacks, 3 of them cannot fight but they still take morale damage. And apart from that there is not much to say. Your troops will be weaker that France's or Prussia's anyway, except if you stack ideas. Lategame, you have western units so you crush everyone not western, even militaristic nations like the Ottomans. But money should win the wars as Portugal, not quality.
Colonization:
Colonization is not that strong right now, but this is still a good way of becoming stronger when your neighbours are stronger than you. This is the historical situation of Portugal and Netherlands for instance. There are several things to consider when deciding where to colonize.
First, and you seem familiar with this, mostly colonize if you can transfer trade towards your homenode. That's why NA is not that important as Portugal, but the Caribbean, South America or Africa are most important. There is an exception if you have a small kingdom and you can reach Indonesia and the Spice Islands. Even without steering trade, the production value of these colonies if you can state them is worth it.
Pretty obviously prefer provinces with high development, but also provinces with good potential tradegoods. There is a bonus for colonies neighbouring each other so try to have colonies neighbouring each other. Also prioritize provinces without a lot of natives or with natives not ferocious because as Portugal you should go for native repression policy; this helps you immensely and you can divert an army there to protect your colonies without much harm because Portugal is safe from ennemy aggression. Use this same army to smash native nations.
The best provinces are thus the Cape, Ile Bourbon and Mauritius, and the Caribbean. Chose provinces that give you access to native nations, they are the easier way to expand. All of this being said, La Plata is not key at all for instance, and the northern coast of Brazil as well. The Eastern coast of Brazil, the Caribbean and Western Colombia are all good however.
The AI usually colonizes at a predictible pace and in a predictible order. Brazil is one of the first regions to be colonized, the Caribbean as well. They should be your priority. At least a few provinces of Brazil because the Caribbean Islands are more important. The AI usually don't bother with Africa until the late 16th century so you can ignore Africa as well, this is a waste of opportunities. The colonies there are also not good at all apart from centers of trades. They are slow to grow because of climate, there are a lot of natives and they are usually low development. The provinces with a lot of trade power are the only useful ones in Western Africa, let Castile or France lose time colonizing the rest of them. Jump to the Cape and Swellendam, for neighbour colonies bonus, and because you don't need any army there because of unferocious natives. Go for Ile Bourbon and Mauritius to take these good provinces and block other colonizers, and go back to colonizing the Americas. When someone starts colonizing southern Africa or St Helena, go for Indonesia, this means they will be there in 10-20 years but with native repression policy you can completely outpace them.
Edit :
Portugal is playable. Really. Especially if you kill Spain. But even without killing Spain. There are no problems with managing colonial nations right now, it's the easiest it has ever been because you can develop their provinces and reduce their LD. This is not a RoM feature if I'm not wrong. Anyway, CN in the Americas are good, but the Spice Islands are better and they also give you FL. They grant you a lot of money even without 100% of the trade. This production value once you spam manufactories...
Should I distribute them to other Trade Nodes?
Do I miss something interesting in this feature
I have no idea how to effort a good army, colonies, expansion and not folling behind in technology.
