Get good, best guide?

[2205]

Pretty sure they shouldn't, otherwise you could buy tons of books and never fail?

 

[Iridium Winter]

I'm 99.9% sure they don't stack lol

 

[Hayleia]

In 4U they stacked. Pretty sure they do here too.
The reason why it's not overpowered is that you can't reasonably bring a whole library in your inventory at each quest so they're mostly useful when not in a quest

 

[18388]

Regarding the weapons, styles, etc. try doing the practice village quests. Besides giving you a more simpler way of testing the weapons, the rewards usually consist of Potions, Well-Done Steaks, etc.

 

[2205]

Good point, I didn't do them again since they looked pretty much like what the demo had to offer, didn't feel like doing them again...!