Thanks, I knew i needed to study up for Friday. I thought if I could preempt migration questions by noting my research, I'd do it. lol
I do recall last year doing a multistep process to upgrade the new phone to the beta before migrating, and finding out I didn't have to actually do that as, unlike previous years, it could be part of the migration. I imagine that's the same this year... .
Regarding your iPhone's mp3 files, I think they get moved over via an iCloud backup, but I don't know. Maybe the phone to phone transfer would work better, again, I don't know.
I'm the Apple expert (lol) to many of my friends, but I have very specific use case for my many devices including using iTunes Match and Apple Music, and friends who use local music files on the Macintosh computers. Most of my work files are in iCloud Drive. It's been a decade since I used my computer or phone like that and have no idea how some of those details work when not totally enmeshed in the Apple Ecosystem. I get a new Mac or iPhone and I have all my music and work files available to download immediately. Slight tangent warning, lol.
Good luck and enjoy the adventure!