By the way, I wouldn't violate copyrights for existing documents, as I wouldn't be selling already copyrighted material.

Now that would take some intelligent decision making on your part to decide which works were actually already in existence, and which ones were new. Add to that that you'd actually have to GET a copyright on every work that you wanted to protect. Even if you wrote it first, unless you had proof you did it (like a copyright) you wouldn't be entitled to anything.
To make any kind of reasonable profit, you'd have to read through them all and decide which ones had already been written, and which ones were actually worth copyrighting. In the end, this defeats the purpose of what you’re trying to do. I think your energies would be better spent using your inventive imagination to actually think up and write a story. THAT might make you a profit.