RE: Rey keeping the books
Perhaps we can interpret it as Luke, a Force user, that has studied the ways the Force was taught and found its flaws but chose inaction; these books should be burned. Rey on the other hand is going to study the flaws of how the Force was taught but choose action and actually apply her wisdom, whether that means redeeming Kylo or craft a new Force Order, or both. Hence these books will have value because it offers a baseline of guidance, but not strict code for future generations.