To reach the level 100 books in any order you must have 3500 Prestige. It unlocks the tab itself and will increase to unlock the other tabs. The max Prestige you can have is 5000 which unlocks every tab.
The only thing that should go down once you're able to buy the book is the Influence.
Might I note it's actually a lot easier to get these books on our server. On the official PWI it takes about 2.5 months. So really that's only a lot on PWI, not here.
