In a 10 gallon reef setup I would not get any crabs. As far as the snails go, Nassarius like to burrow and come out when food hits the water. The ceriths I've kept bred frequently, leaving eggs on the glass, but I never raised any after the egg stage, they became food for the tank. I think you meant to say mini-serpent star - the mini should be ok in a reef tank.
In my opinion, it would be very difficult to create a self sufficient environment in a 10 gallon tank. It's gonna need lots of frequent manual intervention on your part for freshwater top-offs, partial water changes, parameter monitoring (
salinity,
pH,
alkalinity,
calcium, etc) if you plan on keeping corals.
