Hi Infreus, welcome to our forums! I hope indeed that this is the RPG editor you are looking for. If you need specific features, or want to prioritize some features, just let me know.
Of course you will be able to sell your games! I even encourage it and will help you get the word out.
The best way to help me is make a cool game that shows what RPG Playground can do. I’m a technical guy, not really good at designing RPG games, so I hope that you are :).