The only part of your question I can answer is No. 1. The answer to that is YES. I've happily installed on an old HP (T7500 CPU) and and installing on a Dell Optiplex (i5-6500 CPU) almost successfully in the latter case - I'm struggling with CEC so the TV remote can be used.

In general for the other stuff I'd say that LE is a lightweight OS and if you want full OS capabilities you might want to look at a full Linux distro.

Your No.7 is sort of what I'm fighting with at the moment. If you buy a Pulse-Eight CEC adapter (c£40 from Amazon) then your standard TV remote. I have it working on the old HP but not the newer Dell (yet I hope). You can look at a Flirc remote (Amazon have them) or, if you're not bothered about controlling the TV with the same control look at something like this (again Amazon)

iPazzPort RGB Backlit Mini Wireless Keyboard with Touchpad and IR Learning TV Remote combo

I's better for controlling Kodi and has a few TV control keys, I just wish I could persuade SWMBO to use it

Quote from mason

4. Can I install and use FreeTube, or a similar privacy respecting YouTube client?

5. Are there settings to ensure the OS/Kodi uses DNS that I can set?

6. Is it possible to install Firefox and can I install add-ons (e.g. uBO etc)?

7. Is there a decent TV remote style input device that works like a wireless mouse/keyboard so I can plug in the mini-USB receiver to the PC and use the 'remote'?

2. https://jellyfin.org/docs/general/clients/kodi/

4. That's called Firefox + adblock.

5. DNS is set by DHCP server on the network or by static network configuration. Nothing kodi specific there.

6. Only in x86 legacy build. Edit. My memory was wrong. Can't find it in addons anymore or maybe I was confusing it with Chrome.

7. Search for air mouse on amazon.

7. Most wireless RF remotes are USB HID compatible and many have a keyboard if you need that too. No need for a FLIRC unless you want IR, since RF is better anyway and doesn't depend on line of sight.

My favourite with the keyboard is the AuviPal G9S backlite, programmable keys for the TV and rechargeable batteries. Another choice would be the G20BTS since it is IR, RF and Bluetooth but it eats batteries.

Martin