Regarding Album Art, there is an option to save it in as Folder.jpg in each album folder {Tools/Options/File Location/Covert Art > In the same folder as the file (as Folder.jpg)}. I do this even though it uses more disk space but I don't have to worry about it when I move libraries around. The thumbnails still have to be regenerated in any case. My cover art is also saved as a tag in each file which, again, generates some space overhead but I'm willing to take that for convenience.
I serve MC27 from the RPi4 but the media are stored on a NAS (Synology DS1819+). I also run MC27 on an iMac and on the Synology in docker (as backups). To edit the library, I do it on the iMac because on the Pi, editing is painfully slow. ThenI back up the library, move the backup to the Pi and restore there. Works perfectly and all I have to do is reset the path to media and restore thumbnails and it's all good.