I would say that if it were going to be a fish only tank then you would be safe with about 25 inches of fish. That is 1 inch of fish for every 2 gallons of water. I wouldnt put any tangs in a tank this size because they need alot of room to swim. I would get a pair of percula clowns, they are always fun to watch and they are fairly hardy fish. I would stick to smaller fish (about 3 inches). Just my opinion. It also depends on what you have for filtration, and if the bio load with be capable of handling that many fish.