Yes, just buy uncured live rock. I also agree, a small White Blenny or a Pigmy Wrasse. One or two small fish would be fine. Not much more.
I would go with at least 12 pounds of live rock, and I would buy at least one bag of live sand. Most bags I have seen have 30 pounds of live sand, but I don't think you would need all of that for your tank. Just do enough for a 3in sand bed.
When you cycle the tank, it might be easier to just get a uncooked shrimp, and put it into a clean pair of panty hose (Rinse the hoes). Throw that in your tank, and let the cycle begin. The rock that you get from LFS
will most likely be cured already, so you won't have to worry about too much die off, which means hardly any ammonia to cycle your tank. Once the cycle is done, you will just take the hoes out of the tank and throw the shrimp and hoes away.
My tank took three weeks. With this small of a tank you will not be able to get hardly any fish in your tank. Your looking at ONE small fish, and two will be pushing it. A nice Clean Up Crew would be cool to add, such as a hermit crabs and a few peppermint shrimp, and a few snails. But, beyond the Clean Up Crew, you will not have much swimming in your tank.
My advice is, to set up your tank and cycle with freshwater, and throw a awesome looking Betta in with maybe three Cardinal Tetra's. Buy yourself a 20 gallon kit, and get the Marineland Penguin 200 filter (The filters the kits have are crap), make sure you got a good heater as well. The kit will mostly just be your tank and hood. I would add this too it.
Amazon.com: Aqueon 06104 Submersible Aquarium Heaters, 300 Watt: Pet Supplies
You can get the 30 pounds of live sand, and 20 pounds of live rock and set it up. You can than get a pair of Clowns like you want!! There is only a few that can live in a 20 gallon, but they look great, and are hardy. A great fish to start out with! I think the Black and White Clowns are really cool looking! Please read this as well!! Very helpful!!
Clownfish for Sale: Clownfish Species for the Home Aquarium