Presently I have a 3 gallon Pico setup and running. I used established live rock and live sand from another aquarium. The cycle was completed after about 2 weeks. I have tried keeping Clown Gobys in the tank and have not had good luck, they get way too stressed to handle it. With such a small tank there are few places they can hide and relax, they will usually die within a few days. They are also very hard to get to eat, so attempting to feed them everyday is going to spike your ammonia levels in the tank, resulting in a dead fish
Even if you do water changes everyday, the ammonia will raise to lethal levels. Clown gobies are known to jump and will do so if frightened, they are easilly spooked. I used a DIY homemade eggcrate cover and still lost a fish due to jumping. The best thing for a small tank like this would be corals, some cool shrimp, and some hermits. I have a Peppermint Shrimp and two Hermit Crabs in my tank and several mushroom corals. I am not telling you not to do this, just be aware of the problems you are going to run into.