Well if you like information, you'll be pleased to hear that they're working on a wiki for supermechs too.

That would depend on how powerful they are. If they were too powerful, you could just fill up your weapon slots with heat gaining weapons, for example, no one could beat you, because you'd just repeatedly force shutdown your opponents' mechs. If they were too weak, and you only had one, it'd be a waste of money, because their effects are too insignificant.

They would have to have some restrictions, like being rare (expensive), having small ranges, short lasting effects, etc. for it to be fair.

I could see this working if there were an upkeep of sorts. Like say you use one of these weapons for an ACTUAL crippling effect, your opponent cannot move anywhere, but you have to spend one action point each turn to keep this effect in place, however there is only a certain percentage of a chance that the effect will continue, so you may end up using one of your actions for nothing.