Cerith snails are a must have. They clean both the rocks and the sand. There are different species, a good mix is always best. If you have sand then I would add nassarius snails. I got a few giant knobby creepers from reefcleaners.org and have been happy with them, they plow through the sand real well. As do the small conch species. A few turbo snails to work the glass and rocks and you're all set.
Don't forget fish as part of your crew. A wrasse and some tangs will save you a lot of grief.
As to quantities, I'm not sure. I always tend to go light on my cuc because if you add too many they will starve. 4 giant knobby creepers, 2 conchs, and 20 nassarius snails if you have sand. Add another 40 assorted ceriths and a dozen turbo snails to start. That's just off the top of my head. Most web sites that sell clean up crews will have packages for sale that specify quantities. Good luck with your tank!