How about hosting an ADS-B receiver, tracking nearby air traffic. It doesn’t serve any practical purpose other than participating in the crowd sourced network that feeds sites like FlightAware and FlightRadar24 (and you get a free subscription by participating)

As with many others here- Wireguard and public IP. Add to that I can choose between split and full tunnel to either use the connected network for anything not on my network (split) or have everything routed through the network (full tunnel).

Yes, although MySQL/MariaDB or PostgreSQL are the more robust options.

For personal use. As someone who has all my non-trivial creations, including dot-files and scripts I replicate between machines, in repos since CVS has a thing it’s a habit. Version control. This stuff is mostly private but not secret, why should I have it public?

Edit after spell check.

Without knowing what ypu plan is in detail, here’s one example of a plan for a NAS…

• Flash your SAS card or get an LSI card you can flash to IT mode.
• Install TrueNAS Scale and set up your ZFS volume with your existing SAS drives
• If any drive fails, exchange it for a SATA with at least the same size and re-silver.

You wouldn’t need to exchange all of them at the same time as long as the one you are swapping in can hold all the blocks the old one did.

Yeah, your data is taken hostage. When cancelling the subscription it’s a good idea to delete everything manually before the account expires. Even if you can’t guarantee Dropbox haven’t just flagged the files as deleted, it signals intention. I did this when migrating to pCloud and haven’t received any reminders from Dropbox.