Check out some of the stickies, they'll help you figure out how much lighting you might need and give you some other basic info. Corals need more lighting than you'd think, but it isn't too expensive for a small tank... you can check out the coral profiles to find out which ones might work in a nano tank. A 6g is too small for a pair of clowns, you're pretty much limited to one very small fish, like the small gobies. With such a small tank, it's going to need very good maintainance. You'll need to be doing top offs of fresh water every day, to keep the salinity stable.