I've had the best luck with trochus snails as my rock/glass cleaning snails, they're kinda hard to come by sometimes though so the next best snail would be margarita snails IMO. Turbo sanils and astrea snails are also good but can have problems turning themselves over if they fall upside down (astrea snails) or bulldozing rocks and corals all over the place (turbo snails). Nerite snails are also pretty good but they will lay little white eggs everywhere (they won't hatch though). Can't go wrong with cerith and nassy snails in the sand bed. You can also get a tonga fighting/tiger/strawberry/florida fighting conch once your tank matures a bit to help out in the sand bed.
Blue/zebra legged, mexican reef, and scarlet hermits are great for picking stuff out of rocks. If your LFS has some, halloween hermits are super cool looking and also good at cleaning excess food up.
My reef aquarium will also always have at least one shrimp, they can be annoying when feeding corals but they are very good at cleaning up uneaten foods, especially in hard to reach places. You can also get some utility out of a skunk cleaner shrimp in helping keep your fish healthy

currently I have a flame shrimp and it is amazing at cleaning up the tank and looking like a million bucks with its amazing red and white coloration.
I would start out with 5-10 rock snails and 10 or so sand bed snails. After your tank is ready for fish, you can add a shrimp and some more snails if you feel like you need more. Snails are usually pretty hardy but don't be alarmed if one or two don't make it, sometimes they just don't adjust to a new environment or your LFS worker picks out some weaker ones.