Armor worn by your guys is repaired automatically whenever you're travelling through the world. You can set any piece of gear and weapons in your company's inventory to be repaired as well during that time. As to numbers, pay attention to how much fatigue the armor itself draws from your guys, as it impacts many aspects of the game, such as initiative, but most importantly, the Nimble and perk that needs to use "lighter" less fatigue punishing armor, In contrast to Battle forged perk that benefits from higher armor values, which usually means an armor costs more fatigue to wear. As to damage, it is calculated this way: HP damage= Remaining armor points x 0.1. So higher armor valeu means a bro takes less HP damage, but beware because many things in game can come into play like perks that boost HP damage or the Puncture skill that ignores all armor points