Arkham Knight Batman suit painting question

If you skip the PVA and go straight to Plasti, the piece won't be as smooth, but more flexible. The PVA sort of fills the pores of the foam, making a smooth-ish surface, and resulting in a more rigid piece. You don't have to heat seal the foam, but it's a good idea, especially if you skip the PVA. I don't have experience with acrylic paint, but I just went straight from Plasti to spray paint.

Bogleo's right, and I'll piggyback off of what he was saying. I always prefer to use Plasti instead of PVA to give the piece more flexibility. If you use PVA, the paint will be more likely to crack if you move around too much. Here's what I would do: Use a heat gun to start sealing your foam, then Plasti-Dip it. After that, I would go straight to the gray you're planning on using on the armor, and then weather it by hand with silver spray paint and an old washcloth. Does that help?

I have tried several techniques and have found that heat sealing in conjunction with 2-3 layers of mod podge, then layered with about 2 coats of platidip followed up with acrylics works by providing a strong/smooth surface and retains decent flexibility. I've been doing gauntlets and belts using this method and haven't noticed any wrinkling of paint. However if the piece requires extreme flex then you might want to leave out the PVA. I however haven't run across a piece that required that much flex in my builds.
my suggestion would be to try a couple different methods using test pieces of foam to see what your happy with.