Without going too crazy and listing everything... A butterfly; with a moderate to bold diposition, not too ornate or trailing finnage like a threadfin (he'd probably chase it) and not too big adult size, a Raccoon or Pakistani would get too big.
A Zebrasoma Tang, anything except a Sailfin would be ok.
If you get juvis they should all grow to a fairly good size, the angel about 8", the others about 5" each. You'd be right at the 1" per 5 gallon range.
Butterfly first, then the tang, then the angel.
Personally I'd pick a either a Saddleback or Blackback Fly, and a Scopas Tang.