There’s always Cryptosteel’s Capsule. Marketed more towards crypto wallets, but absolutely useable for our purposes too! Personally I just have mine backed up to Proton Pass. I also have a copy on an Apricorn secure thumb drive, stored inside an encrypted pwSafe database, inside a fire safe… lol
I sync my password database every month or so. Be sure not to let flash memory sit too long. The cell charge tends to dissipate over time. M-Disc would probably be better, but I update mine often so it has time to refresh the cell charge.
I use Dropbox to backup my photos, and Restic to backup my Camera Uploads folder. If you want to use a free Dropbox account, and have limited space… throw Rclone in the mix. Have it move photos out every time the backup script runs, then have Restic immediately back it up. Worst case scenario, even free Dropbox keeps your deleted files for 30 days. 
Don’t clone. I learned this the hard way. You’ll end up cloning corruption before you notice it. Just look at my most recent thread here. I’d have never, ever noticed this if I was just cloning my repo. Use independent repos. Compare the output / diffs from simultaneously(ish) run backups on occassion. You never know…
Honestly, this one is more at your discretion (aka paranoia level) lol. I do occasional checks. Maybe a full --read-data every 3-6 months.
Also kind of more about your own comfort level. I use Homebrew on my Mac to update Restic, but the same concept applies. I call it at the beginning of my main backup script. And I’ve absolutely been affected by the stray bug or two… but I’d have likely done that manually, too. And by Restic’s design, the absolute worst it would probably do is corrupt THAT snapshot, and not the others. I haven’t seen that happen, but for the most part Restic only appends data, unless you Prune / Rebuild / etc. I’m not too worried about it.
I use a second cloud. And M-Discs, for the super important data (mostly my photo collection and tax documents, for me). With everything RAR’d and PAR2’d to the literal brim of the discs, to boot. 30% parity. And multiple copies, at different locations, of course.
Yep!