Sunlight isnt at all a bad thing so long as you keep the Direct sunlight from beating down on the tank.
Cory cats are not algae eaters, but are omnivores. They are scavengers and eat bits of food in the bottom of the tank, but you wont find them sucking algae off of the glass. They like meaty foods like bloodworms, or even beef heart if you chop it finely. They also eat vegetable matter like bits of lettuce, soft peas and zuchini. Normal fish flake should be fine, but you can sure supplement their diet with the other foods to keep them at optimal health. They can get up to about 3 inches long, but they stay small for quite a while. If algae becomes an issue, you might look into some of the freshwater inverts such as some snails or shrimp. Ghost shrimp and snails are omnivores but also eat algae. Ghost shrimp should also work well with Platys and Mollys. There are also some dwarf species of Plecostamus that dont get very large, but they are hard to find in most stores. The ghost shrimp are relatively easy to find and cheap (depending on your location. They are about 20 cents each here). They get about an inch long, but they like to have babies too. Most of the fry get eaten unless you have a good hiding place for them or remove them from the main tank. If you chose freshwater snails, keep in mind that some of those get real big as well, 3 inches on some of those monsters.
Youve really got a handfull. Mollies and Platys in the same tank. Those are probably the two easiest to breed fish. Both fish give birth to live young, they dont lay eggs, but Mollies can give birth even after being seperated from a male fish for months! When they get older, they can birth a hundred or more babies!!! Hopefully you have all females and they wont continue to do that on a regular basis.