As Portugal, you benefit from an end node in Sevilla. Provided you take Tangiers (and maybe Southern Spain with the help of France), you should control 50-80% of the trade power. There are two important nodes which directly lead to Sevilla : Caribbean and Ivory Coast. So start by colonizing Cape Verde ASAP and then the Caribbean, the islands are very wealthy and fast to colonize. Send the trade to Sevilla or collect there if you lack trade power in your Capital. Take Bermuda too if you can, this will cockblock Spain and England and delay them for years. When this is done you have two options :
-colonize the nodes leading to the Caribbean (Mississipi, Panama)
-colonize Fernando Po, fabricate claim on Benin and take control of Ivory Coast. Eventually you'll want to settle in Gold Coast for the TP bonus. Try to reach 51% with the trade company (don't put all provinces inside it, because as Portugal you also need manpower. Just put Benin/Gold Coast inside the TC). Then you can start the trip around Africa and eventually to the Spice Islands...Don't try to colonize tropical provinces at the moment, they take too long.
Some remarks :
-Brazil (and La Plata) are ok to colonize (you play with Portugal after all), but stick to the non-tropical part of it.
-Let Castille/England/France have fun in NA, you have no business there
-An alliance with France will be necessary if you plan to kill your competition early in the Caribbean
To answer your questions :
-"When colonizing South America, should I aim to form a colonial nation as fast as possible? Are they working properly in 1.8?"
CNs work like in 1.7 except that you don't lose prestige any more because of the elections. They have also buffed the naval AI (this is cool for the Caribbean islands)
- "When colonizing Africa, the best strategy is create trade companies all the way to Asia? Are they working properly in 1.8?"
Yes, and yes
- "How many provinces should a Trade company have?"
Just put the provinces with bonus to TP, add some more with TP buildings if you fail to reach 51%
- "Caribean, TC or CN?"
You can't have TCs in America