Do note on coral nipping, my moorish idol did completely wiped out the zoanthids in my tank, can it be they taste like sponge? Didn't cause trouble to others though.
My best advice to you is to make your tank bigger. At least a 300 gallon tank. I started wanting a 240 and then actually bought a 300 gallon an craigslist but then had a custom 450 built. The fish love to hide in the caves when they feel threatened or chased. Plenty of room is always good especially for a school of Moorish Idols. Go big or go home!