Idk about lg pleco and molly, but the snails will just it the dirt/poop and the shrimp will clean up ,too. The shrimp might also eat the fish food so...
For the molly a tropical fish flake or pellet would work. (I Use tetra color with mine). Also with mollies you can give them a few freeze dried blood worms with the flakes once a week as a treat. For the pleco it depends on what type you have. Most of them like to snack on wood so I would get a piece of drift wood. Some plecos will feed on extra algae in your tank. If you have no algae you can buy an algea wafer plecos will also eat.. Snails will also eat algae wafers and algae along with extra flakes/pellets left over from the mollies. As for the ghost shrimp they will eat a sinking pellet or tablet made for bottom feeders along with extra food left from the mollies.
Clown plecos are an example of a pleco that loves to eat wood and won't eat much algea.
I have tropical flakes for my fish which will then sink to the bottom and my plecs wil eat that but i also give them algae tablets which i got from my fish shop
