The type of photography you are aiming to make money out of thrives on network. The more people you know, the more likely you are asked for a job (there’s no such thing as job adverts for event photographers).
You also want to build up the nicest portfolio you can. I suppose the question is, how good a friend is this and how well connected are they? For them to set up a festival (however small) with 29 acts (oops, not so small now!) means they have connections elsewhere.
I would choose the amicable route, have a chat (now) explain how much work is involved and share your thinking with regards to the costs involved. Your time doesn’t have to be free, but payment doesn’t have to be in money either…
There isn’t a right or wrong answer, early on you will have to balance favours with work. I shot some professional events for my job and they (to my surprise) led to several other requests that did offer fair payment. It’s the way you build things up.
THose are some stellar names. Awesome find. You could almost open a photography gallery with that sort of quantity and quality.