If you need re-stumping, it is much better to do it before any painting/plastering or all the money you put into that will be wasted (because they will crack as the house subsides, or when you get it restumped). I think it is also better to wait 6 months or so post restumping, to allow all the walls to settle before doing the plastering/painting.

Not sure what the plaster is that you have.

I agree that it sucks spending money on restumping, when you don't really get to see any benefit, but it will help all your later renovations stay and look good.