There are so many options.... If you plan on having any snails (which I highly recommend), I'd stay away from blue or red leg hermits. They have been known to gang up on snails & kill then for no apparent reason other than to do so (seen it). Scarlet hermits are great reef friendly crabs. As far as snails, my favorite cleaners are astreas....great appetite for their size. Nassarius snails are good for cleaning & stirring your sand bed. You also have to get a couple of shrimp in there!! They are very cool critters to have in your tank.... recommend skunk cleaners. When they get comfortable, they will be out all the time, where fire (blood) shrimp tend to hide during the day. I'd stay away from banded shrimp.... they are really cool looking (wish I could have one myself), but they can get really aggressive as they get older.
Start with a couple/few of each, and add more as your tank matures. If you dump a whole pile of CUC into a new tank, there's really nothing for them to eat yet, so you have to worry about keeping them fed as well.