Hi,
Just looking to get some feedback before I purchase hardware:
Alternatively I was considering an old surface tablet… but they are smaller, and who knows how reliable really…
Surface tablets, providing it works for you are built like tanks. Reliability wont be an issue. The charging circuit in the device should handle always on OK and the surface drivers handle battery conditioning on Windows, so always on shouldn’t destroy the battery.
Also if you’re not planning on running HA on this and are only using it as a display almost anything you mentioned will be more than enough. You really only need enough horsepower to run a pretty mediocre web browser experience. If you’re going to display a lot of video or media then it becomes more critical, but the dashboard itself… Nah.
I run mine on a 5yr old Fire 8HD. Even with occasional display of a security vid from Ring or Arlo.
That’s cool. I bet the Surface would handle things just fine, although a recent experience with one suggests they aren’t super reliable. A refurbed one would also be a risk I suppose.
The setup I have here would run off a pi zero or something I have hanging around just for display purposes. Although 
I do have a wireless hdmi link I am not using, heheh. Could just plug that into the pi running HA and link it to this display.
I also have an old ipad 2, but it seems they really don’t work.
So I ended up buying a waveshare 15" touchscreen display. It was only $150 or so but it broke twice after a few months.
Now I am looking at something a bit more expensive and hopefully more reliable.