If you haven't got a nursery tank a small percentage will reach adulthood. Small ornaments with in and out entrances give them some protection
Mollies aren't notorious for destroying plants, so what other fish do you have? Plecs are known to eat plants though certain plants can survive, it's a matter of choosing the right plants. Floating plants is another option depending on what is destroying what you are buying. Plastic is an option, I've got a couple of Oscars that like to rearrange their tank and plastic is the only thing that will last in with them.
Most of the pet stores that stock live plants have somebody behind the counter with a degree of knowledge on the subject, but it's often a case of adapting what they have to what you want, put an African Sword in a well lit 5 gallon tank and you will never see the fish.
Edit: Emms has the Molly breeding bit covered, the only thing in your tank that will actively destroy plants is the plec assuming because you have a plec the catfish are Cory's.
I feed mine cucumber, blanched cabbage leaves and occasionally peas, but that colours the water. All fish will have a nibble at cucumber and the swords will eat cabbage once the plec has done the hard work and created a raggy edge.
I only feed my pair of L137 greens, it's cheaper than buying plec tablets and algae wafers as they are eating the same things as me. Mind they ate all the real plants first.