Tough to add multiple clowns at different times, they tend to kill each other.
I have 11 spotcintus in my 100 (all added at once), a pair of lightning maroons in my 50, a pair of phantoms in my 20 nano and 10 mixed captive bred Ocellaris in my 40 grow system. With the clowns that all came from the same batch or are just single pair are fine, even the maroons, who are notorious for murdering other clowns.
The mixed clown tank is a constant battle with the smaller ones getting beat up pretty bad. I have to separate them a lot to prevent causalities.
Now pairs of other types of fish, go to town... wrasses, lyretail angels, anthias, reef safe triggers, tons of options.
If you do add more clowns, try to get a lot of nems and feed them a lot to help minimize territorial aggression.
Good luck, whatever route you go!