Is there any way that you can buy body armor then be able to wear it on an actor? like on Darlos's Darkstorm where you need the ammo in order to fire the gun... but instead of the restriction purpose, you just put it on for the protection...

If you want armor added on the arms/legs that actually bends with the limbs, you can forget it.

And unless the actor is specifically made to be able to pick up this armor, it's going to look screwy. Soldier helmet inside a giant robot's head, arms overlapped by vest, that kind of thing.

If I remember correctly, limb armour works fine except for the fact that the arm armour tilts with the head. Other than that, it works fine. See Exalion's SCRAP for an example. It has perfectly working leg armour.

This.
Arm attachables are really the only kind that suck for the reason above. The best you could hope for is a shoulderpad, and even that could look stupid.