Compatible with Red Hairy Legged Hermit?

I have a Red Hairy Legged Hermit in my 30 gallon along with reef hermits and snails, as well as an Emerald Crab. I'd like to add some more inverts but am not sure what would be compatible with this aggressive crab. Does anyone have any experience or suggestions? I'd like to add a shrimp or two and another kind of crab, maybe a fish eventually too. My crab is about the size of a large egg (including shell).

Thanks for the help!

VTEEL