If you have a normal tank, you probably have low light, so head for plantgeek's "low light" section.
Java fern is a good leafy plant that doesn't require much other than a rock or piece of driftwood to attach to.
If you've got fish, you probably don't need fertilizer, but most plants do need iron. You can either provide this by adding a plant-specific substrate, or by using nutrient additives.
The snails probably hitched a ride on the moss, and are probably not mystery snails. They're probably common pond snails, and are pains to get rid of. It has been kind of determined on the boards that the only reasonably effective way of getting rid of them is to add a snail-eating fish to your tank. Otherwise, you can learn to live with them (not so difficult, as long as they don't eat your plants or hurt your fish

)