the idea of selling your armor is nice. you could buy the armor you have, and when you get to higher ranks and better armor, you could sell the armor you bought at the beginning of the game and buy the cooler armor you unlocked
all of the ideas are great , and i only have one thing to add. You should be able to choose if u want a wall to bend when hit. for example, if you hit a wall or structure with a warthog or a banshee, it could bend or bust open