This is unorthodox, but I use https://www.overleaf.com/ its a neat online editor where I can have my docs stored on the cloud and it has a PDF preview on the side, and you can compile it at the end.
LoRa fits the low power and its also long range. I have never sent images over it but for sure its possible but unreliable, as its very low bandwith.
I would do some kind of computer vision to identify people, or count them and send that data instead, those operations should be easy on a microcontroller.
I agree with the NUCs, a good compromise ive found is the Lattepanda Delta or Alpha.
I don't have a Pi 400 but I have a similar cyberdeck that has the addition of a screen with the keyboard and board. I use it as a swiss army tool on the go for managing my cloud servers. Its like the classic monitor and keyboard you have hanging on top of your rack, but portable :D
I think I had the case with jet2, where support for a change of a cancelled flight required my CVV, I called them and told them that I am not willing to provide that information and they should figure out something else. They instantly replied that I can input anything on that form and that it didn't matter and so was it.