At the last puzzle it's not hard it's just frustrating because you are randomly looking for something. If you gave the key for "free" the player will know that they need to find the keyhole. And for moving the book maybe all books are align except for one, the player will find it odd and try to play with it. I like the style, keep up the good work! I also did a puzzle game for the jam. Here if you want to try: https://itch.io/jam/gmtk-2019/rate/463579