5 questions about mollies?

1. I found solid white mollies in the pet store, and I tried looking for them online but i havn't found anything like that, just high fin mollies that are white, but the ones i found are short fin, is that unusual? 2.would it be okay if I just had 1 molly with lots of platys and guppies? 3. do mollies really need salt, i've seen people have no salt in their molly tanks 4. I've read mollies love live plants in their tanks, but I only got fake plants, lots of them, Would that be okay? 5. I have an aquarium ornament with algea stuck to it, it wont come off, should I just leave it on so the mollies can eat it?