looks like a very solid backup plan. One thing i am not sure with the xpub backups is that since it's xpubs... they can't be really backed up offline or by hand writing....
They can, it's just a tedious and unfriendly process. Print out the xpubs on the same piece of paper where you will write down the seed by hand. You can even add lines for where the seed words will be written later.
Backup: 1. _____ 2. _____ 3. ______ etc., xpub 1