I think you should have 2 “shortcut” buttons

Yeah, I think having sensible defaults would make a lot of sense and it is not hard to implement.

UI-wise, I’d try to implement a page where you can see all the artists you want to support, and each of one them would get a slider scale. It’s (relatively) easy to program it in a way that the payout distribution percentage is preserved even if you add/remove artists.