As always, Biff is right on. Get a variety for your cleaning crew and if you do go with hermit crabs (I would), make sure you pick up some empty shells that you throw into the tank. Hermits are lazy as far as seeking out snails to kill. They will choose the empty shells when they need to grow (hermits do not make their shells, but snails do) unless they have no alternative - then they will kill your snails and take their shells. When your few additions have survived a week or so, add the rest. Aim for a critter per gallon when you are done. Do have a serpent star and a cleaner shrimp or three when your tank has been around for about three months. Be careful with peppermint shrimp, many fish like sampling them - make sure your fish are not going to eat them. Mysis is great food and better nutrition than brine shrimp, I like also using frozen plankton (not reef plankton- there is a difference. Frozen plankton is larger), it is great for enhancing the color of your fish. Good Luck.
-Dr Marco :sfish: