I like your idea of using a foam mold.  I am curious if you will be using a mold that is basically a mold of your body or one that would be the exact opposite: a mold of the armor.  If you were to use one that is a mold of the armor then it would be very easy to get a smooth finish as long as the mold itself is smooth.  Think of it like mache-ing a ballon.  the "outside" is kind of rough from the texture of the paper and glue but the "inside" is very smooth because it was up against the smooth balloon surface as the piece dries.

If you are doing it the opposite way then I would recommend using many layers of regular office paper or news print to get strength.  Then as a final skin use blue Scott Shop Towels (available at Home Depot, etc.).  This is the best thing to get a nice finish to layered paper mache.  This stuff is the greatest discovery for paper mache that I have seen.  Make sure you tear it instead of cutting it with scissors.  The jagged edges make the seems between pieces almost invisible as the towel paper almost melts into itself.  Use either wallpaper paste (it usually has anti-fugal/mold additives ) or thinned white glue and a paint brush.  Once everything is dry give it two coats of white glue and then Gesso and paint and then seal to make it waterproof. :twisted: