Absolutely no lionfish! A clown trigger will definitely pick on a lionfish, even a volitan is a bad choice with a clown trigger in such a tank like a 75.
The fish that you would be okay with getting are most type of groupers, puffers, eels, and maybe a few species of bigger wrasses.
Tangs (except for a Sohol tang), butterflies, and angels are out of the picture with a clown trigger in the tank.
Definitely try to get a bigger tank if you are going to keep a clown trigger though. You will have much more room to work with getting tankmates for him.