You could put one or two in there. I have 3 adults in my 10 gal and theyre making babies all over the place!
Just make sure you give them rocks to attach to, some like them to attach to glass but they moved all over the tank when I tried that.
I feed mine 2x a week with mysis.
Good luck
Clowns won't host rock nems. Sexy shrimp and porcelain anemone crabs will. They're a lot of fun. There's room but some like to move more than others. Clowns will be fine.