I agree that Percula's will host with some strange animals. I have them going to a Stichodactyla haddoni carpet, a Heteractis magnifica, and even to large feather dusters. They also like Goniopora corals, which I try to discourage although mine haven't seemed to harm them, so far. I have been told they can, however.
You can keep 2 clowns and anemone display in twenty, but constant monitoring would be a must.
Chemistry changes can come awfully quick in even twice that amount of water.
Good luck.