Okay, given that AI models need to look over hundreds of thousands if not millions of documents to get to a decent level of usefulness, how much should the author of each individual work get paid out?

Congress has been here before. In the early days of radio, DJs were infringing on recording copyrights by playing music on the air. Congress knew it wasn't feasible to require every song be explicitly licensed for radio reproduction, so they created a compulsory license system where creators are required to license their songs for radio distribution. They do get paid for each play, but at a rate set by the government, not negotiated directly.

Another issue, who decides which works are more valuable, or how? Is a Shel Silverstein book worth less than a Mark Twain novel because it contains less words? If I self publish a book, is it worth as much as Mark Twains? Sure his is more popular but maybe mine is longer and contains more content, whats my payout in this scenario?

I'd say no one. Just like Taylor Swift gets the same payment as your garage band per play, a compulsory licensing model doesn't care who you are.