In the end it's always a balance of security and redundancy, isn't it? You can't really have both.
Absolutely. If this is your chosen set up, then the only thing I can see to add would be to airgap your computer, if it isn't already. Encryption at rest is obviously a good thing, but if you are decrypting on an internet connected device, then there is still a potential risk there to your descriptor/pub keys. I have a handful of different multi-sig wallets which I use for storing larger amounts of bitcoin, but the computer involved is always airgapped. Once the transaction is fully signed by a combination of computers, hardware wallets, whatever, then you can load it on to an internet connected computer to be broadcast.
My back ups for a 2-of-3 multi-sig take the following form:
Back up 1: Seed A, xpub B
Back up 2: Seed B, xpub C
Back up 3: Seed C, xpub A
That way any two back ups are sufficient to fully restore the wallet, while the compromise of one back up provides the attacker with nothing useful. Using this system, I don't also have to back up my public keys elsewhere, as you have done in your password manager.
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....
You will have to either print it out or keep the file in a digital form..
Meaning, if a person uses a multisig setup, he will likely backup the xpubs or the whole setup of his multisig in a digital form.