Armrests look great. I like screwing them on from the backside of the panel with no glue or anything. That way if they need to be repaired they can come off easy.
I use 1/8" landau for everything. If you cover the armrests in foam I would make sure to block sand the foam with some 80 grit. From my experience even the thin 1/8" foam will really soften the edges and change the look of the armrests.