I have 2xAsterea, 6xNassarius, 1xfighting conch, 3xMexican Turbos (2 turbos would be plenty for rsm250). And I have many Cerith and many Nerites (too many to keep track of for both cerith and nerites, I replenish these once a year). I also have some hitchhiker snails, collonista(s). I also have three species of hermit crabs, 3x blue leg hermit, 3x red leg hermit, 1x Hawaiian dwarf zebra hermits. Shrimp are also great for cuc: I have 2 skunk cleaner shrimp and one peppermint shrimp.
Agree with Di, wait until the tank cycles before adding snails/crabs (do a huge water change to bring down the nitrate levels).
Add nassarius and shrimp after first fish - they both help to clean up uneaten fish food and fish poop.
Agree with Glenn, add half the amount of snails at first, then add the rest 4-6 months later, the reason is that you want to make sure you have enough algae for them to eat. If you add your whole cuc up front, there may not be enough food for all and you will end up loosing some to starvation.
