Try checking out reefcleaners.org. You can custom build a package there for you aquarium! I like trophys snails, margarita snails(hard workers!) dwarf ceriths and Nassirus snails
For the sand. Gotta have a cleaner shrimp too!!!
You could get a few snails if you want, but I personally find that CUC is overrated. In my 40g I only have 3 nassarius, 3 trochus, 1 hermit crab and 1 fire shrimp. That's it. Your real CUC are the little guys that came with your live rock, such as worms, brittle stars, colonistas, etc. Don't overthink it, not worth it IMO
In a tank that size, I would probably start off with about 5 turbo snails and maybe one scarlet hermit. See how they do for awhile and then adjust the population accordingly. Hopefully if things go right though, you won't have to add any more janitors to the tank. You can keep the glass and the sand clean all by yourself. GL.
Monitor the peppermint shrimps, caught mine eating out of my brain, plate, and Aussie favia mouths. I got rid of them, and my hermit crabs. Hermit crabs will kill snails, and themselves for a new home, even with bigger shells laying around. I would stick with snails, cleaner shrimp, and a sand shifter goby, maybe a emerald crab not sure how reef safe are they.