The number of fishes goes down when doing a reef tank. Two tangs are a "no-no" in a 75g. Damsels may get too aggressive when introducing other fish. I like clowns, maybe one tang, and a dwarf angel. Put the clowns in first since they are hardy. Wait a bit (couple of weeks-month) to introduce the next fish and then introduce the tang last. If you go with a different route, you want to introduce the most aggressive fish last. Good luck.