I think Clowns would be okay in your tank. I think the amount of fish you cann keep depends on a few things, their adult size, and their temperament, etc..
As far a CUC goes:
I can't help a lot there, but I do have a tip.
If you get any Hermit Crabs, make sure you have some extra shells lying around for them to move into. Otherwise you will probably run into the crabs killing snails and other hermits.