Instead of perk tree and level cap I would give different perk cost (1 point for 1 tire perk, 2 points for 2 tire per, 4 points for 4 tire perk) + every perk needs proper statistics, and perk points only for 2/3 levels (1,2 level perk, 3 level no perk, 4,5 level perk,6 no perk, etc). In that case there is no weird restrictions and your battle brothers will be more different. Of course this should be balanced against munchins :)
