I heartily approve, without much help to offer. Points of thought…
-Calibre web server good, mirror Annas Archive best, practically somehow getting everyone’s downloaded books into a community Calibre would rock.
You’re going to need a bigger NAS (Jaws pun, but seriously, this will be at least / more important than your server, redundancy is king)
Probably something lighter / easier too maintain than Nextcloud for simple filesharing, Seafile perhaps?
Honestly, this is the sort of initiative that could drive local Mesh adoption.
What security are you using, most govs/corps don’t like private internets, how vulnerable are you to CSAM etc.
I’m aware of a fair amount of local sneaker net approaches (HDD swapping etc), which mostly avoids the security issues. I too would love to hear about successful use cases.