If you're here, get a Tarsnap account. This gives you backups however you script them. They're versioned, deduplicated, and NSA-resistant.
And while I've got your attention, 1) are Arq backups encrypted and 2) can it back up via SSH to my own storage somewhere - like a cheap VPS with lots of disk space?
2) Yes. Although if you're after cheap space, Hetzner's storage boxes are the cheapest $/GB I've seen (https://www.hetzner.de/hosting/produktmatrix/storagebox-prod...), with Backblaze B2 close behind.
Compare that to Backblaze or CrashPlan, which do all your PCs for $5/month.
Not really. Those 4KB with the encryption key are EVERYTHING in full disk encryption. There's nothing equivalently important in unencrypted disks.
FDE further complicates things, though, as if the volume master key is corrupted everything is lost. If my hard drive dies, there's a decent chance that a data recovery shop can recover at least some of the data.
Or, if you are stingy and/or enjoy a bit of occasional sysadmin DIY, get a Linux box and configure it to look like a TC. There are plenty of tutorials out there, it's very easy.
Time Machine likely makes sense for laptops, though it's got low storage capacity at the price.
If you have a Mac, get an AirPort Time Capsule. This gives you automatic, hourly backups. The importance of automatic cannot be overstated. If you have multiple Macs, they can all backup the same Time Capsule.
You can save a little money using an external hard drive, but how often are you (or your family members) going to remember to plug it in and run Time Machine? Once a week?