There are a ton of options for you to stock a 75 gallon with. You'll just want to mostly avoid larger fish like large angels, most tangs, etc.
It really depends on whether you want your system to be reef safe or not for us to make recommendations. Here's some types of fish to look at:
Wrasse: most fairy or flasher wrasse are reef safe and optimal in size. Just make sure you have a tight fitting lid as they are known jumpers.
Dart fish- same as wrasse really.
Hawkfish- several species would work here, just note that they aren't always friendly to inverts.
Almost all common gobies, blennies, cardinal fish are good additions. There are a ton of fish to choose from. Feel free to look online and ask if your favorites might work back in this thread.
A few species to possibly avoid:
Basslets/dottybacks- cheap and hardy, they can be highly aggressive and merciless in a 4 ft tank to peaceful fish.
Damsels- same as above.
Anthias- much more difficult to care for than your pet store will lead you to believe. Really need more space than this, and lots of feedings through the day.