WRT 3-2-1 I’m only part way there for my personal stuff, I haven’t been willing to invest in anything offsite yet but gained some peace of mind anyway. Offsite backup for the most important stuff is in my future for sure. FWIW here’s what I have, and what I did:

In order of size: 1000+ movies, a couple dozen TV series I may want to revisit, something like 10000 songs (mostly in albums), and a slew of scanned family photos and genealogy documents as well as offline ancestry databases.

In order of importance: family photos and genealogy stuff, music, movies, TV shows.

I ended up with a primary NAS, Synology 4 disk with one disk redundancy, and a second older Synology set up the same way that serves as backup. Each with battery powered UPS. The older NAS has degraded twice over about 12 years, and each time I popped another disk in and a couple of days later all was good. They do scheduled data scrubbing and I subscribe to an inexpensive SMS service that texts me when that gets done or if anything else happens.

I don’t use any backup or replication software. Anything on there started on either my desktop or my wife’s laptop, and we just copy it twice. Except the TV shows and the one-and-done Netflix movies, they just go to the primary and I assess later if they are in need of backup.

Hope that’s useful in some way.