Usually, rule of thumb is 1-2 lbs per gallon....I think there IS such a thing as too much if your fish have no room to swim LOL Unless you want a rock tank?
The more rock you have, the more bacteria your tank can process. There is a balance though, eventually there can be too much for some fish to swim comfortably.
Yep that's the general rule. When I started my biocube I had 58 lbs. In a 22 gallon area and to me it was way too much rock I took out several pieces to make more room and a few months ago I took out even more for more open space swimming.