i would remember that if you invade a province capture and destroy it and then leave the next turn, then their is a very strong chance that provience will rebel with a loyalist army of it previous owners. all of these high tech loyalist rebels are going to be very pissed at you and may invade you.

it has been my experience that you need to leave a large army of atleast 700 troops +priests and spies in a provence for about 10+ years before you can safely abandon with out getting a loyalist rebellion of previous owner.

so be aware that raping and pillaging gives a good amount of cash but also gives your enemies lots of high tech armies with which they can use against you.