May I suggest capping the max level/money/exp to be much lower? It's pretty fun to have some of these insane upgrades, but the fact that you can have basically infinite money and exp means you never need to make any real balancing decisions, as you can eventually totally max out everything anyway. Furthermore having near infinite money/exp generated is what leads to people eventually becoming almost impossible to kill. I think money should be capped to an amount that allows you to max out two stats at most to be honest, that way you might actually have to choose between offensive and defensive capabilities.
Also, as much as I hate to say it, disabling caps is probably for the better when the exp/money system relies solely on killing people, as capping just leads to a period of free kills, ergo free money, and then a snowball effect, making it easier to cap next round.