Livestock suggestions

[Kryten]

Well, my 30", 24 gal is almost ready for some livestock. I'm looking for suggestions for reef-safe fish. I'd like something that will help keep the substrate clean a bit, and then something small, colourful, and active for the feature fish. Are clowns best kept as a pair, or would a single one be happy?

Also, wasn't sure if this counts as a nano, so I posted in Reef.

Thanks!