I watched a BRS video (series maybe?) on Youtube once about starting a clownfish harem tank. I am not sure how that would work in the long term, I would not put more than two clowns in my 220 gallon...
As long as clowns are all added at the same time and are the same family they can do well together. If 2 do end up paring off it is likely they will kill the other clowns in the end.