Post how you want on your project, its ok, its your thread lol. Your sizing looks right on to me. As far as sanding and bondo go, its kind of a personal thing. To me, the armor seems to be somewhat angular in game, so it should reflect that in the piece. And for curvature, bondo, sand and repeat till youre happy with it. It looks like it wont be much of an issue for you though lol. The 2 ways are apply a little bondo at a time as layers, sanding as you go, or apply a thick layer and dig the details back out. I prefer the first method.
I hate to let you in on this cause your pep work is great, but foam is much less expensive and comfortable and easy to work with. You can get almost the same results with foam too. However I still use pep/bondo for hard items like helmets.