i have 4 clowns in my tank .i have 1 anemone. pretty much only 1 ( the female the larger one )spends time in it. but they will do fine without one as well .so it's your call. i will tell you this ,some anemones wander alot mine finally found it's spot and has been there for quite a while.so if you have corals and suck you don't want disturbed don't get 1.
Get an aquacultured fish, they are usually healthier than wild caught specimens. Also, clowns don't need an anemone, they will do fine without one. Sometimes they will host in corals or something that resembles an anemone, and sometimes they won't host at all.