Yes you can keep that mix, but its a little much for a 120, go with a valentini or false eye dwarf puffer, 1 dogface, 1 porcupine puffer, and 1 other fish. Thats a good mix, I have seen 3 puffers in a 40 gallon tank, a dogface, S&S, and a dwarf. Of course this wont work for life, but its a good start.