stomatella and collonista snails will breed in ur tank like crazy, but they are small and i dont think much places will sell them, they are ussually hitch hikers from live rock.
stomatella and collonista snails will breed like crazy in your tank, but they stay small and usually arnt for sale, they are usually hitch hikers from live rock. i dont know if this counts as a snail but limpets will also reproduce in your tank.
It depends on your lights bro. I would go for about 1 snail per 2 gals of water and get a variety so that they exploit different environments,"stay away from bumble bee's if you want inverts."
To answer your question the s.w. snails have a lot more babies than fresh water snails . However their larvae have a planctonic stage and they don't do well with impeller blades so I'd be rather surprised if any of them ever survive.
hth
Max