A couple snails, a couple hermit crabs. Just to start off with. I always like to add CUC to my tank as i see fit. If i see that my current crew is keeping the algae down, why add more right? If algae and detritus start to grow out more, then you know to add more. But don't go and add like 10 more hermits and snails just because of a little algae growth. Add one or two and see where that brings you. You would be surprised at how much algae and detritus your small CUC will eat.
For snails you could go with, Nerites, Ceriths, Dwarf Ceriths, Astreas, Trochus. And for hermits you could go with just about any small hermits you can find at your LFS i guess. I never really kept a preference on hermits. Some people say that hermits will kill snails for their shells, so just beware of that, as it is in some cases true.