I personally would not offer the artist a cut from what you earn promoting their music, but the other way around; When they come to steemit, you take a cut from what they earn! That is how it should work IMHO. Well, best way is maybe just try to get them to Steemit and whatever they earn, they keep. So, selling the idea of Steemit to someone, is a mix of things: They must like blogging, they can use Steemit for various purposes, to promote their own work, ideas and whatsoever, what they do on Facebook they can also do on Steemit. Steemit can just be another social media channel they operate. When they don't like to handle social media, well, their bad, they will not come to Steemit.

No issues to feature someone else work, it is curating as so may websites do. I suggest to add some good writing to the music you feature, objective review, your personal opinions, maybe some links to there social media and all. I personally like the personal opinions and stories around music posts, so when I see msuic post with generic stuff about the artists/band, I get bored and skip them for reading. To many other places on the Internet where you can find that. But not so many places where you can read personal stories around music.