MTS are probably the best for keeping sand turned over, though assassins would do the job as well. I've never had any problems with MTS in sand tanks; it seems to be only in gravel tanks they get out of control.
Snails can be kept on their own, although most of them will be already carrying eggs and/or sperm when you get them!
Just sand is fine for plants, although you do sometimes need to pile a few pebbles around them for a couple of weeks, until they've rooted in. You could try sieving the gravel out, in the tank, with a cheap plastic sieve.
Personally, I don't think sand really needs turning over at all; it's just that you can see the dirt on sand and are compelled to keep it clean , whereas with gravel it's all hidden.