JonathanS OK, well thank you for your replies and leave it with me! First I need to learn if I should install the ST2 backup to ST3 before or after I add the MP3s to the app. And if I can share playlists from iTunes directly to the ST3 folder.
If your songs are in the media library you can just restore the backup. If you imported your songs from Dropbox, you need to copy them from Dropbox into ST3 via the Files app and then restore the backup.
You can import playlists from iTunes. If you import more than 10 tracks, ST3 will automatically create a playlist (with a generic name). So to import a playlist, add songs to ST3, select all songs in the playlist and after the import, rename the playlist. Tracks already imported will not be imported a second time but they will be added to the playlist.
JonathanS By the way, once tracks are imported to ST3 do the originals need to remain on the iPad? I'll keep many for while I'm using ST2 but I'm not sure I have room for both longterm.
No, you don't need to keep them in iTunes once you are sure you don't need ST2 any longer.