It depends, that's why I've sprinkled my replies with words like "generally" and "maybe." Certainly if a soldier POP is not getting its Life Needs it is likelier to join a rebel group. However, it's CON may be high too and you may just be hostage to greater desire for political reform. Keep in mind in this game that sometimes past decisions take some time to have effects on POPs and how they develop desires, etc. If you can keep plurality and CON low for some time you may get lucky and find POPs more desirous of social reforms, thereby allowing you to retain a more controlling state (if that's what you want).
It will take time to increase your soldier POPs. Try to diversify where you recruit soldiers from in order to not put too much of a burden on one state. That way when you suffer casualties your whole army won't be undersupplied for soldiers. Also, depending on who your enemies are you should be able to build up a smaller, high quality standing army supplemented by your mobilized reserves (what's your mobilization pool?). In recent games as Germany I've probably had a standing force of some 10 30,000-men armies (100 brigades). That, in addition to my reserves was more than enough to deal with France or Russia (I loathe mobilizing, if only because it means organizing so many brigades). I've fended off both opponents at the same time with reserves - it's all about how you pick your battles. You're not too far off from that with 70 brigades - just be patient.
Do you have an immediate goal for which you need the soldiers? If you've just recently united Germany you can probably hold off a few years while you consolidate your gains.
Whenever a box pops up giving me a choice between increasing POP militancy or consciousness I've been always choosing consciousness, assuming it's not as bad as militancy. But it seems like they're both bad choices leading to the same result. In my last game as Japan that box must have popped up 100 times, for the same state. In another state a box popped up over and over again which gave me the choice of higher militancy for the whole state or just one of the provinces in that state. The result was their militancy was at 10 the whole game. No matter which choice I would have made, they all would have had over 100 militancy if there was no limit. There's nothing you can do about it apparently.
Yes I'm shifting the soldier focus from state to state but it takes a few months for one unit to become available, and you have to leave the focus on that state for a few years to get the benefit of it. I don't think there's going to be enough time. I'm the USA in this game. I already (1840s) got tricked into a war with Prussia and there's no way I can do anything to them except blockade them so they can't get to me.
I'm no good at Great Power wars. I understand you're supposed to destroy their armies but rarely am able to do it. They always escape and come back at me. You need a ton of troops available to surround them so you can destroy them, but those troops are always busy fighting off attackers and defending territory so it's impossible to get enough in one area so you can surround the enemy. I need to figure out how to get a ton of troops. There's mobilization but it's a mess like you described. In this game, I'm getting like 4 or 5 units available a year, by putting National Focus on soldiers in New York, the most populated state. That isn't going to be enough to take on Mexico and the CSA, forget about the UK...
Question: after you capture a province, do you still have to keep blockading it, or is it irrelevant and you can use your ships elsewhere.