Hi there and welcome,
You've come to the right place for anwers...that being said your questions are very telling, are these things you've discussed or are you just curious? Because as with monogamous relationships there are no guidelines to speak of, just what works for the particular relationship.
To answer your questions specifically:
1. This board is excellent for poly reading, I encourage your boy to read it too, both the new to poly threads as well as the blogs; couples who have been where you are before are great sources, as I found them to be.
2. You're human in a relationship; you have rights same as his girlfriend. I found the maxim of "fair but not equal" to be a good idea when starting out. In this case it means that because your coming into an established relationship you should expect to be treated fairly but understand that his girlfriend may set boundaries. Intimacy is not synonymous with sex, emotional intimacy is real, and if you feel like you might develop feelings (sounds like you already have) for this boy you need, need, need to discuss these things with him and with his girlfriend.
The worst thing you can do for yourself is assume that you are inferior in the relationship, but you must understand that you might have to adhere to the boundaries set by others. That is second to not communicating, if you make assumptions about how available emotionally and literally he will be for you it will end badly, again you need to discuss this with him to set clearly intentions, boundaries, and guidelines of what happens if someone has issues that need addressing.
Polyamory is wrong! It's Multiamory or Polyphilia. Mixing Greek and Latin roots? That's wrong.