I think you may have misread the message you replied to. The message you replied to was implying the Russians wouldn’t know how to deal with the kernel because they can’t shoot missiles at it. That’s the opposite of what your reply implies.

Upgrades are easy, backups are really good, if upgrades mess up, you can restore from backup even if NC is hosed. As for local storage, I never did it, but here’s the docs for it! https://docs.nextcloud.com/server/latest/admin_manual/configuration_files/external_storage/local.html