I don't recall the name of the book, but IIRC it gets put in the quest item section of your inventory. It is the book the librarian gives you for finding the book be was looking for. If you have not completed that quest yet, it is in a locked chest in the chamber with the bedrooms upstairs, and IIRC the key is in Amdusias' secret room.
I read the book in the library, and I assume anywhere would work, or at least anywhere on that level in Maxos temple.
You can sell or destroy any common books or any plants / ore you are not going to use for potions or enchantments. Keep any malachite gems you have, but any other plants/rocks can be easily replaced once you have the battle tower.
If you have the spare skill points to put in the Encumbrance skill to increase your inventory size, you can re-skill after you get the battle tower, when you will have ample storage.
Have you summoned your creature to help in the fjords? After taking care of Amdusias you might want to try reaching the next level before heading to sentinel island (to get a full level for a mindread during your first encounter there). Trying to take out a group of level 21 imps in the fjords at level 17, I did much better with a ranger head (level 2 Fireball) than warrior (level 6 Rush Attack / Fatality). I was almost level 16 before entering the fjords; my first fight brought me to 16, and working my way down the mountain trail (level 18 goblins) brought me to 17. Clearing the next beach and swimming over to another, both with level 18/19 black ring members, almost brought me up to 18.
