Question, does the game have a guide on the different routes and paths to take?
Is it possible to be a good student and a slut at the same time?
Do tattoos and piercings change in-game conversations?
1. No, I was working on one but got too busy (and the game changed very quickly). I will be writing one when things are a little more stable, but for now, if you have questions, feel free to ask here and I'll answer where I can.
2. Yes, absolutely. Your "sluttiness" is driven mostly by her Easy trait, and to a lesser degree by her Risky and Excitable traits. There are others that come up from time to time (you need to have low sophistication to do a couple more socially frowned on acts), but those are the big three. Your academic performance, on the other hand, is dictated primarily by your Stability trait and your Learning and Discipline skills. It may take a bit of careful work to raise the traits required to be a slut while also ensuring you'll be a good student, but it's not impossible and they're not in opposition most of the time.
A good way is to have a mother who is too young, a happy (or at least non-abusive) home life, then join the nerd social group. From there, make sure she focuses on an interest in boys/girls/hot people and have her activities involve the library and hanging with friends. When she defines her reactions to male attention, make her as open and accepting as possible.
Do those things, and you should be well on the way to a well-adjusted geeky girl who has a
lot of sex. Remember birth control if you don't want some life-altering decisions.
3. Rarely. They'll change descriptions of your PC, and there are a couple scenes that have offhand mentions, but otherwise they don't have a significant impact on the story or how your character is perceived. I suspect that having a lot of identifying marks might be relevant during the spy part of the story, but that remains to be seen.