1. I'm not sure about this kind of question too. Did you already check your free space of a drive that the game located? Or another way, I suggest you to move your game folder to another drive (or folder).
2. I think It default that you can't use rollback thing in this game. Since the dev don't give us "Back" option for the first time. And if you have encounter with "nameless", I'm sure you will understand.