Becoming an advisor to a start-up while working full-time

Like the title says - I'm in a fortunate position to be serving as an advisor to a start-up while having a full-time job. The founders and the team are pretty capable and they are very self-aware of what they are good at and what they're not good at. They also have a realistic PoV on what their mission is and when to stop trying.

Couple questions are -
0) One of the founder is my friend. How do I serve his interest the best while gaining experience on my end?
1) Who do I need to reach out to in my company to go over any compliance and conflicts of interest related matters?
2) What are the things I should be aware of when it comes to my reputation, career risks, and obviously $?
3) What should I expect from this experience?
4) My biggest worry is there is another advisor who compliments my skillsets, knowledge, and personality. I believe I need to act as a bit of a bumper in case he goes off. What should I know to serve best as someone who balances things out?
5) My other worry is that perhaps not everyone is aligned on how far to take the company - luckily, it is something that has been discussed and the expectation is let's work on this for "18 months and then see what happens". As an advisor, is this something I should worry about at all?