Who said SH are meant to be alone??? However, here's how I roll:
IMHO, snails are fine (you need a mix of different types). Some peeps keep hermits, but I've seen even scarlet reef hermits (the most docile) grab tails, so no crabs at all as far as I'm concerned.
Instead of crabs, add a few true peppermint shrimp (about 1 per 10 gals to start). Stay away from "cleaner shrimp" as they tend to stress out the SH due to their insistence. Likewise, eschew CBS because they just get plain ol' nasty when they get some size on them.
Stock most snails at about 1 per 3 gals to start, then adjust once you see what your tank "needs". Stock Nassarius at 1 per 10 gals and wait on turbos unless you have a HA problem, then go 1 per 25 gals.
Stay away from margarita snails unless you run your tank below 68*F, they'll die at warmer temps.
HTH