A few words on bumble bee snails... they are carnivorous and will kill and eat all other snails that they can.
I lean towards snail heavy CUC's. I like Nassarius or Cerith for sand stirring cleanup duties. For algae reduction I like Trochus or Astrea snails, Seahares and small Mithrax crabs (once they age they become carnivorous, get them out when they start on corals). Yellow cucumbers are the only ones I would consider as they are the least likely to cause tank wipeout. The scarlet legged crab (with yellow eye stalks) is also the only hermit I would consider as they are the least likely to kill and eat snails. Tuxedo urchins are probably the best urchin to choose because they are "less likely" to bulldoze and knock things over. Saying that, I have a small rock boring urchin that doesn't cause too much trouble. I personally like the small red serpent stars. I find them less likely to prey on fish. They clean in places where many other animals can't reach. Don't forget shrimp. They are THIEVES!!, but IMO have a place in the system. Fire shrimp have been IME less likely to be as bold about thievery. Peppermint shrimp are probably the most beneficial IMO. I have three skunk cleaners that I battle every time I feed the sun coral. We usually end in a tie. They steal a little, but not too much, so we're both happy. Scott mentioned porcelain crabs and they are just danged cute! Beautiful little buggers and a gem to have in the tank.
Starfish ... well, they can be difficult. Forget linckias, they need to stay in the ocean until we understand their diet better. Fromias may be a better candidate but not by much. Starfish are difficult to feed and need EXTREMELY long and careful acclimation and are extremely sensitive to chemistry changes. They are best left to a very well established, large tank owned by an advanced aquarist. (I'm not saying that you aren't one, if you are then get a starfish, but you're asking this question so...)
So, snails (a variety)-about 1 per 3 gallons. Sea hare, 1 per 30 - 50 gallons. Mithrax- 1 per 10 gallons. Red serpent- 1 per 10-20 gallons. Shrimp-1 per 10 gallons. cucumber- 1 per 50-100 gallons. Scarlet hermits- 1 per 5-10 gallons. Porcelain crab- 1 or 2.
My cleanup crew in my DT 75= 10 nassarius, 6 trochus, 1 nerite, 5 mithrax, 2 seahares, 2 red serpents, 3 skunk cleaner, 1 fireshrimp, 2 peppermints, 6 volunteer stomatella snails.
CUC in the 55 fuge: 6 scarlets, 6 blue legs, 2 serpents, 6 bumblebee snails
HTH!