Not OP, but I can answer part of your questions:

if I migrate to Jellyfin do I need to fuck around with my folder structures ? No special case just /movie/title | tv/title in my use-case with the usual arr stack for grabbing.

I have Plex and Jellyfin running off the exact same media library no problem at all. So there should be zero need to modify anything–if anything Jellyfin seems a little better at catching “extras” folders than Plex.

I don’t need remote playback for movies/tvs but I have no idea how to replace Plexamp and if you have suggestions, feel free to mention it.

The Jellyfin app plays music–but it’s definitely NOT a music app. I always hear Symfonium highly recommended, but have not yet given it a whirl myself.