first, i'd keep an eye on that hermit you have. it's probably going to eat whatever else you may put in there.
i'd start out with 10 astrea snails, 10-15 mixed hermits, 10 nassarious snails, 1 (and probalby only one total) mexican turbo, maybe a bristle star if you notice a lot of detritus in the tank, and an emerald crab or two.
that would be a good start, and you can add snails as you see fit based on algae on the glass and rocks.