IMHO, forget the puffer, and add a Pterois russelii lion (often sold as "red volitans", which is wrong). Think about a foxface or rabbitfish, maybe one of the medium/large scorpionfish such as Scorpaena brasiliensis, maybe even a Rhinopias frondosa (weedy scorpionfish) or an Inimicus stingfish (pop-eyed sea goblin).
I guarantee it would be a cool tank of uncommon fish.