If it were my tank I'd probably round it out with a pygmy angel (cherub, flameback, or whitetail as they stay small), some sort of prawn goby for the sandbed, maybe a banggai or other type of cardinal. Those occupy different strata or have different habits so should work ok together. A firefish would be another option, and neon gobies are always a good utility fish for the cleaning services they provide. I'd suggest a longnose hawk, but it would probably eat the peppermints.
I'm not sure about mixing clowns in a tank that size, though...