well a reef involves corals so you'd need real god lighting. pc, t5 (aka expensive crap), or halides would be necissary.
there's no stingray that i know of that will fit in a 55, dwarf lions are a possiblilty but not the regular ones. for clowns and tangs you are looking at the lerger species (if you want the lion) like sebae, cinnamon, fire, tomato, blues line, maroon, and clarkii and pretty much only yellow tangs are sutible for a 55 and that debatable.