welcome to the party, @5chickens! great name, by the way, lol
to answer your questions in order (note, I don’t do much festival editing, but I do work with a fair amount of events)
- I don’t know that we have a relationship for this yet… there is an Artist-Artist relationship for supporting members, but as far as I know nothing for Events. (tho see point 3 below)
- in general, I’ve just noted these in the setlist and add the collaborators in the relationships. that said, if there’s a release by the collaboration, that should be tied to an actual artist (or perhaps if it’s more than a one-off act as well)
- again, I don’t believe there’s a relationship for this yet, but there is a ticket for a new relationship: https://tickets.metabrainz.org/browse/MBS-13817
on the j-idols question, that’s a tricky one… I believe in general, these should be added credited as their name in the group. for example, in Family Force 5, all the artists went by aliases (you can hover over or click through and see that for example, Hollywood’s artist name is Teddy Boldt)
that said, I work in the adjacent realm of vtubers, and the general practice there is to keep idols in an agency seperate from their “indie” alias (tho that could just be a vtuber thing, since there’s a lot more emphasis on the privacy of the artists)
(related thread: Of VTubers, agencies, and unknown legal names)