A pair of Centropyge or Paracentropyge would be a fantastic centerpiece. Arguably perhaps the atlantic longnose butterfly Prognathodes aculeatus, at only 4-5" could be okay. Again borderline on size for a burgess, but another possibility. Wrasse like a mystery, flasher, fairy, or halichoeres. Depending on the level of care anthias like the ventrals, blotchy, or bartletts could be good showy fish. While limiting on your other stocking options, Golden Dwarf Moray eels could be decent. Similarly a marine beta, given no small fish.
Lots of fun options in that sort of tank! any special interests? Caribbean, Australian, African? Deep water? Predator? Deep bodied, long bodied? Reef safeness? Budget? Difficulty of care? Peacefulness? Tank mates it needs to be compatible with? Captive bred? So many different directions that a show fish can take a tank, and vice versa. It's one of my favorite parts of the whole build process, picking the fish that everything is going to work around.