Start out with a controlled amount at first. Maybe only 3-5 of each, snails, hermit crabs, other types of crabs, etc.. Then add more as you need them. Also don't forget that hermit crabs and snails sometimes don't go together. It's a known fact that hermit crabs will kill and eat the snails for their shells when they feel like moving out of their own shell. I know there are people that have both and have never had this happen, but there are still sources out there that have this documented. Just a little word to the wise.