+1 Alex
If you are dedicated about it, you can train them to eat frozen, which is much healthier than just feeding them the feeder shrimp throughout their life.
But, like Alex said too, they will try and eat anything they can fit in their mouth. Considering you are going to do a 55 gal, he will probably be able to eat most of the fish you can put in that size tank. You could do a predator tank and do the frog fish, maybe an eel and a dwarf lion fish, but the clowns, and other attractive fish will most likely end up as lunch.