Questions about my tank?

I have a big 10 gallon tank, its got alot of oxygen, a 30 gallon filter on low current and a smaller filter with an air pump. I also have a heater that adjusts by its self but stays at about 78F all the time, anyways I have 3 Betta's, 2 male, 1 female. I was thinking putting the female in the newly set up tank (it has plenty of bacteria and everything) with some other live bearers. This is everything Im putting in: 1 female betta, 2 male guppies, 1 black molly,1 silver molly and 2 platys. I know theres enough room because I wont be breeding them. Do I need aquarium salt for it? I was wondering, would it be better if I put one of my male Betta's instead? And also would I need more fish to outnumber the mollies, because iv'e heard they like to go after the smaller fish. thanks