How books work in this game? Are they completely seperate from each other or is there some connection?
I mean, If I pick Slave route in B1 will it affect future events in any way?
The answer is yes and no. Generally spoken, choosing love or slave route are the two main choices of the game that will affect the ending. But you could play the books in any order and probably wouldn't even notice any difference right now as the game asks you which path you took. This will probably change in the next patch though, and you have to play through the game at least once before you get the choice option.
quote by Marty:
... I'm changing FET so that if you've played through it at least once, you'll get the option to skip to the Nagina/Spirit choice when starting a new game. You'll get a yin/yang sign at the start. ...
Despite what I just wrote, there are some decisions that matter if you play the books in the right order (1>2>3>4). In some very rare cases, characters will know of certain actions you took in the past or remember you from earlier encounters.
My advice, if you are heavy into story or an ATLA fan, at least play the books in the right order, it's not a huge mistake if you don't do that though.
Be warned though, the difference between love and slave route is significant for books 2,3 and 4, I recommend playing all 6 of them at least once.