i have 3 green chromis in my tank along with a
cinnamon clown.
the chromis are very docile, and hyperactive swimmers and eaters. they dont mess with anyone else.
not sure which species of clown you have, but it's been my understanding that clown are more territorial/aggrssive towards otehr clowns.
i THINK the chromis should be fine. also, if you have a tank that will support it, it would be best to get three or more, as they are a schooling fish.
also, in regards to getting mroe, i've read that with any schooling fish, it's best not to get an even number. that way, they cant pair up or whatever, if there is an odd number (3,5,7, etc..) it's better because there is always one odd man out, so it's better for the social behavior.