Hello everyone, I am getting a new 20 gal tank tomorrow and I'm considering buying a few mystery snails when it is set up and done cycling.

I already have 4 platys and 5 mollies, I was wondering if mystery snails breed heavily or not. Also what do they eat typically?

Mystery snails or Apple snails as they are also called will help clean your tank. They eat what ever your fish leave behind. They crunch it all up and turn it into dust pretty much and send it up into your water column and into your filter.
I have these snails in with my African Cichlids. They're great but if you have loaches your snails will not last long at all

Not particularly since they need both a male and female. If you get a few, the chances are good you might get one of each. They don't breed like the other common varieties available such as bladder, pond and MTS.

As for food, they will rasp on any algae that's in the tank and clean up the excess food from the fishies. Suppliment thier diet with high calcium feeds for optimal shell health which is vital.