I have never had luck keeping mollies in fw. I have kept them fine in brackish, or full saltwater.
Anyway, about the plants. I have a brackish tank for my Red Claw Crabs, a 10 gallon tank and 15 watt aquagro light. The salinity is 1.004. I have Java Moss, Java Fern, Cryptocoryne Wendtii, and Duckweed all growing great. I've tried Corkscrew Vallisneria and Brazilian Waterweed, not sure how they would do, my crabs ate these plants. I've read where Corkscrew Vallisneria can withstand some salt.