My LFS had two sizes of the nassarius, $0.99 or 1.99 size, I went with the bigger snails for 1.99. If you have a nice established sand bed, then I'd get about the same as me, or at least like 3 or 4. Are you getting hermits? I would definitely get like 6 or so dwarf red legs or maybe a few scarlet hermits if you can find 'em(my LFS never has 'em). I wouldn't worry about them killing any snails, since the nassarius will be hidden, and the turbos are too big a shell for them...