Greetings,
Unsure regarding assets you create in the software, I would wait for input from Justin before deciding to do that.
Regarding your second question, which I assumed to mean you were asking about licensing for distributing/publishing a game made with the software: https://rpginabox.com/faq
Quote: "You are free to distribute and sell your games, with no strings attached (i.e. no royalties, licensing, or fees). Although it isn't required, crediting the use of RPG in a Box is always very much appreciated!"
Bear in mind the above applies to the actual game you would like to sell. If you have music assets or art assets from another source in your game you would have to seek licensing information from the creator of the asset. (I.E if you use music from Kevin Macleod, you have to license it from him or attribute it under his Creative Commons license.)
