I think most folks touched on the main ones as well as what you posted. The Librem 11 could potentially be something else to look at, but not sure about the German layout and price is above budget. Theoretically you could also look at doing a Steam Deck with a bluetooth keyboard, although the screen may be a bit on the small side, but would be well within budget even with buying a separate keyboard.
Personally I haven’t had much experience with Linux based tablets. I would say the guy who mentioned converting the surface 3 to a Linux tablet would probably be the best bet for the set of requirements you’re looking at
Yeah I had the exact same thought - “huh, transparent case and charging led” - but I hear they’re going to come out with an update to adjust the intensity of it, so that may help that.
I also upgraded from OG 512 - personally love the OLED so far. Screen is really nice, battery life will be great to have on my business trips, and the clickiness of the Steam and … buttons is a definite improvement. Do you need any of these things? No… but they are really nice things.