Well I have live rock and one hermit, the nem which I'm getting rid of, and a peppermint shrimp that is what I have in my tank. I as far as filter I have an Aqueon something... Circulation pump and heater..
OK, thats a pretty decent start. If you happen to have a pic of what you have going on so far that might help. Liverock is an excellent source of filtration, if you have enough of it in there.
The reason I'm adamant about holding off on corals is because they are extremely sensitive to changes in water quality and...as mentioned before, in a smaller tank it doesn't take much to hose your water quality down horribly...and unfortunately corals are extremely expensive. Would just hate to see you invest a bunch of cash only to find that you weren't able to find that equilibrium between "Stocked enough" and "overstocked".
As for adding the fish, I would suggest adding one fish initially (once the 'nem is out). Let it be in there for 24-48 hours and start testing the water. See if you get a spike at all of ammonia/nitrite/nitrate. Most likely you will see those numbers go up slightly and then, hopefully if you have sufficient filtration, go back down. That's what these folks mean by "cycling" the tank again.
Once that cycle is over, you can add a second fish...and again, check levels. You shouldn't see that same kind of spike again, however, as the tank is then "cycled".
The short explanation of cycling is, for the record, essentially letting the tank build up a sufficient amount of helpful micro-organisms to help keep your stuff clean. This "stuff" will live in the tank, in the live rock, even in your filter.
