Taking Humanism to avoid revolts is perfectly reasonable. I find it to be remarkedly useful once the serious land grabs start as it typically triple taps: fewer religious revolts from unity and tolerance, blanket unrest reduction, and perhaps most importantly separatism reduction. It is often my third or fourth idea depending. My point is more that enduring the Reformation alone is a poor spend of an idea group. Staying Catholic, even with Humanism, makes killing off the centers highly lucrative as well. If you can vassalize England & Scotland, reduce them to 9 non-colonial provinces, disconnect their capital from any provinces with > 10 dev, or leave only with provinces with >= 10 dev that are in the area with the Scottish center that can help your lands stay Catholic and get some of those nice Council of Trent bonuses (e.g. +10% manpower in True Faith and institution spread) by strangling Anglicanism.
Killing off the center in Scotland may be worth two wars. If their capital is the center, then just force convert them once they flip ASAP. If it is not, take all of their provinces with higher dev than the center or isolate them (so they are not connected to other provinces). You wan the highest dev province in their largest contiguous block of dev to be the center. Then when you take their cap, the new cap is with the center. Next War is a force convert. If Scotland is not supersized, you may get decent cash along with a force conversion/dismemberment. This is again one of those things that gets much more lucrative depending on how Trent falls out.
You may well have better uses of your time and soldiers, but a 10% manpower boost in a province is pretty decent.
For you PU, mark some provinces in Portugal as critical. You can have your new PU junior expand there, and more importantly get you some cheap colonial nations (for the merchants) and overseas toeholds. Depending on who Portugal is allied with, you might be able to let your PU handle all the fighting and mainland sieging while you steal land in Africa, Asia, and the odd colonial nation capital. Having more merchants makes it much easier to get increasing rates of return on trade flows, getting at least footholds around Africa without wasting colonist time is also huge. If Portugal has a big enough colonial empire it might be worth while to eat them in Asia & Africa and then chew up Europe until you can annex them to snag all their colonies at once.