FWIW, 200% overextension by eating up Brazil makes it sound like your absolutism is sitting at zero or something. Don't increase autonomy in late game unless you really must, so as to keep your absolutism as high as possible. You can stack up to 40% administrative efficiency through tech and high absolutism. That will reduce your coring costs and overextension to the point where you can gobble up enormous swaths of development in a single war.
For aggressive expansion, keep the mechanics in mind: you need a) 4 nations b) with AE 50 or more that c) hate you (negative opinion), d) don't have a truce with you, and e) feel they can beat you by forming a coalition against you. You get more AE based on geographic, cultural, and religious proximity. That is, closer distance = more, similar or same culture = more, similar or same religion = more. (HRE is yet more, but it doesn't matter with your game plan; unjustified demands are yet more too, but you're presumably using an advanced CB.)
The immediate implications of that are that 1) it doesn't matter if up to three European powers have huge AE against you, so long as there aren't any nations that have high AE against you and no truce; 2) dutifully track when truces end if necessary, so as to declare war when they do before coalitions form to begin with; 3) a dead nation can't join a coalition, so once you start slaughtering a culture/religious group, the correct thing to do is to eradicate it before moving on to the next culture/religious group. If all else fails and you end up with a large coalition, don't forget that you can break it up through proxy wars, by declaring on coalition members' allies.
