I would definetly get the damsel out of there after the cycle finishes. Or you won't be able to add anything else.
I cycled my 10 gallon then added a perc and a few crabs and snails. I got a nice little mini cycle after that.
I may try to get another percula clown once this cycle finishes up. Or a firefish...I haven't decided. I will probably get another clown to keep mine company.
A 20 gallon would support a couple clowns and 1 firefish I would think. You will just have to keep a close eye on everything. I check my tanks twice a day and I have 10 gallons of distilled mixed water ready to go just in case.
I setup a 10 gallon salt just because everyone at my LFS
's said you can't. So I did. It is doing very well also.
38 gal SW
, 40lbs base rock, 5lbs live, emporer 280, bio-wheel 330,tronic heater, 2 O. clowns, 1 firefish.
29 gal FW
, boring...soon to be salt I think.
10 gal SW
, 20lbs LS
, 20lbs base rock, 1 unhappy domino damsel (he was in the 38...switched the percs and the damesel recently).