Well, according to the inch per gallon rule, 30 1" fish. for example, you could have 30 neon tetras. But this rule has been broken many times and many have had success not following it. If that's your ideal stock list, I would go for two gouramis, 12 neon tetras, 4 mollies, and 4 guppies (make sure they're all male, otherwise you'll constantly have fry) I'd leave out the "suckerfish" simply because they tend to produce a lot of waste, and almost never get enough food or the proper diet.