I wouldnt suggest the banded shrimp for a 9g tank... my bro-in-law had one in a 12g tank and it was just awkward-looking. Even though the shrimp doesnt get too big, its claw-span is pretty wide and it's antennae are very long... it just looked too big for the tank. As far as snails and crabs go, 10 of each is WAY too much. I would get one or two nassarius, one or two astrea, and a hermit or two. Make sure to have a couple spare shells for the hermit or they may kill the snails for their shell.
Jesse