I will give you a little push if needed:
Checking the lowest part of the Central Tower Area again might be a way forward...
Certainly! There are two other books, one of them is in the Dungeons area (Corris's first major area)
The second one is also in town but only after finding a girl at the top of the ruins area (there is also a CG scene to unlock)
After that, a major event can be seen after beating the final boss.
Good luck! And thank you for playing! I'm glad you enjoyed!