I agree with most of what nu-nu says. Clownfish will be fine for this tank. I would recommend them as one of the first to go in there, as long as you let it cycle and do the 10+ pounds of live rock. I have kept a clownfish and a yellow watchman/ pistol shrimp pair in a 3 gal for 7 months now and they are happy and healthy. Firefish will be good, as long as it is covered, they WILL jump. You can have more fish than most people recommend, as long as you let the tank establish itself. You can do 2-3 fish + clean-up crew in the first 6 weeks. After 6 months you can do another 1 or 2, as long as you keep up with water changes and they are compatable. Just make sure they are small. Royal gramma, scooter blenny, hover line, clown goby or shrimp goby (1 or the other), maybe a six line wrasse, cardinal, pseudochromis, and a few other good fish would work. Along with some real cool shrimp and crabs.