I have a 12 gallon Nano-Cube! If you don't want to run into problems later, then less fish is better. If this is going to be fish only with live rock, then you could get two of the fish you metioned, if you want the firefish, then you should get the goby becuase the are both more timid the the perc. If you want a reef, then only get one of those fish. The inverts sound good. Hope I helped.