First of all (like carey said) you should wait at least a year before getting an anemone, they are very sensitive and need stable water conditions. In a small tank it's even more important to wait. Also just a warning that anemones grow very quickly and get very large. I had one in my 28 gallon nano and it destroyed a lot of my other corals, I ended up having to remove it. If you want it for the clowns to host you should consider getting other corals. Clown will host a lot of different corals, like mushrooms, frogspawn, xenia, ect.
If you want it just to have an anemone you could look into getting a mini carpet anemone, they stay small and come in a variety of colors. Clowns have not been known to host these though.
In post #9 iDream meant to say 1.5 - 2lbs per gallon.
Like mentioned, dwarf angels are known to pick at corals, sometimes you will find one that won't though.
Do you know how to cycle the tank and all that?? A fishless cycle is strongly recommended on this site by most.
Also what kind of lighting do you have? This will determine if you can even keep an anemone.