Butterfly's can and willl eat corals. Mostly soft corals in the anemone family. They are not considered to be reef safe. You will get others that say they keep them successfully in a reef but I would not chance it.
If you're thinking about doing the coral thing, make shure you've the proper equipment first. As for the butterfly fish you can always post on our "trade or sale" forum and possibly get something towards your going to be reef set-up. Good luck