Rabbit snails will eat live plants, just rinse the goldfish substrate, in a bucket, you can use it or mix usually not any issue. If you were a master planted tank person it could be more critical. Try looking up nano fish. Boraras brigittae are very small, also called Chilis, mine have never bothered any shrimp. My sundanio axlerodi blue neon probably would, as well as green neons, eat little tiny ones.
I wold not do a junior size or adult Mystery snail because the dead snail can seriously mess with water quality. Nerite and or ramshorn would be fine.
As previously stated adfrog will anything it can fit in its mouth and they can open wide for a nano tank inhabitant.