I know enough to be able to run a pen drive windows reinstall, but how do I wipe the PC if control has completely been taken from me?

You boot to the usb drive, and when asked what kind of install you want, select custom, from there delete all partitions, leaving only unallocated space, and install windows normally

If it’s your main email address and you use it for most things, then yes, they have access to your devices, and everyrhing else in your life

If i understand correctly, you’re using a powerline adapter, if you can, try having both the router, and the pc connected on the same circuit breaker, powerline adapters are kinda finnicky, you might want to just get a cable from the router to your pc instead

You could just comn3ct via VNC, teamviewer, or any other piece of software to it, if you need hardware access type of speed, try out a kvm switch

Personally i use a pc, and imo if you’re ok with controlling your tv with a wireless keyboard instead of a tv remote, this is the best solution

My parents use a smart tv, but they rely on my local plex server to watch anything other than television and netflix, and imo there’s no point in having those as 2 separate systems if you’re the only user anyways