It depends on how many Mollies fish you want to have in your tank, a 50-gallon tank is just good to have around 15 -20 Mollies fish, if you want to keep more fish you need a larger tank.

From what I've read, mollies are good tank mates for swordtails, platies, angelfish, and corydoras catfish. Please make sure to consider the size of your tank to make sure that the fishes will have enough habitat space.

Snails and shrimps are good tankmates for them as I have asked my grandpa. Check if they are truly good though as he tells from his experience.

We had Mollies with Neons, Guppies, Swordtails and others. There were two tanks about the same size and each had a mix of fish in. You do need to think about the size of the tank but incorporating different fish will be attractive on the eye.

You are right to consider the fish that you put with them. If the mix does not include predators then your Mollies should be fine.