First question, is your tank cycled? If not don't add anymore fish until it's cycled (if you don't know about cycling I will gladly explain
Definitely add more cories when you can, they will be much more comfortable. And I wouldn't increase your numbers by too much, and honestly mollies should have a minimum of 30g because of their activity level. Platies and mollies have huge bioloads, so stay on top of water changes.