I have been tinkering with a cyberdeck for a while now for off-grid usage, so this is a nice find for the hardware side. My main battle lately has been building out the software side; primarily Kiwix (https://www.kiwix.org).
I was originally trying to set it up as the Kiwix wifi hotspot. But after playing with that I decided I wanted the pc to have more than one function so I switched to regular Linux with Kiwix.
So now instead of just Kiwix; I also have my handheld radio programming software (CHIRP), ATAK Server, microcontroller dev environment, copy of Collapse OS, etc.
Does ATAK (FreeTak I assume) run pretty well? Are you just saving everything to the sd card?
I have had a similar project set bouncing around in my head. I have some LilyGo LoRa radios arriving soon to see how well Meshtastic works as an alternative to internet.
I am running the Pi from a solid state hdd as I don't trust the sd cards. ATAK/FreeTak does run well on it. Funny you mention LoRa as I am using exactly that. I have a bunch of the TTGO T-beams (915 MHz) that I have paired up with old Android phones that run entirely off the T-beams/Meshtastic. They can be slow at times for messaging, but it really depends on the channel setting (short range vs very long range).