Since areas within the world are level based, then it should be fairly easy to make it so Cyseal vendors have spell books requiring character level 1-7 e.g., and then Silverglen could have 7-12 and so on. Then they could just unlock all books for the appropriate character levels wihtin each area.
Another way is to allow the unlocked Elemental areas in End of Time to have at least 1 of all spell books, maybe at an additional cost to make up for the availability.
Regarding the whole hybrid class thing, I think hybrids are really strong. I ran a Ranger/Water/Earth/Witch and Knight/Air/Fire combo last playthrough, which is a lot of combinations. It was quite tough early on, but after level 6 no matter the fight, I always had an appropriate respons from both characters whereas Madora as a pure warrior often was locked out of the combat due to bad placement of fire, poison and the like.
My only problem with hybrid characters right now is the Ability level requirement on gear, where Strength based weapons and armor require at least 2+ more ability points that a Dexterity or Intelligence based item of equal item level. This design choice is simply something I don't understand, I find it very odd that mages and rogues/rangers can use items dropping of a monster their own level, but warriors are required to wait 2-3 levels before they can use their items (unless they are not hybrid ofcourse). Whether it should be one way or the other, it should be equal between the different ability classes in my opinion.
