Welcome to the forum!
I wish I knew more about predatory fish but I don't LOL
I do know however that a yellow tang wouldnt be very happy in a 75g. There are several tangs that could be added though, you might wanna check out Aquarium Fish: Tropical Freshwater Fish and Saltwater Fish for Home Aquariums
, they have alot of fish listed and their requirements including tempermeant and tank size.
Theres also alot of triggers listed on that site so give it a looksie!
What about a wrasse? If youre going fish only with no corals you have a really large selection of fish to choose from!
Let us know what you think of. I'm also in the process of deciding what to add to my 125g but I have corals so I'm a bit limited.