Sounds good, yes you'll definitely need to secure the magnets well, especially if the rare earth magnets come in direct contact with each other. Those little critters are strong!
Looks great so far! Maybe try to scale the bicep down enough to allow free movement so it doesn't bump and scratch the chest armour as you move around.
Very nice, love the surface finish. I second the idea of using a hard-hat liner inside the helmet, they work great and can be really comfy. I've worn helmets for hours on end at conventions thanks to a trusty hard-hat liner.