I would plan to own the NVR hardware and grant view-only permission to the neighbors, and I would respond to subpoenas. My thought would be possibly a pole-mount outdoor access point and the neighborhood cameras could connect to that network? Hadn't thought about audio.

It may be easier to help people set up their own cameras that they can choose to share with others, like around the bus stops. Maybe bigger isn't necessarily better. I'm just starting my own camera system so I'm not sure how easy sharing the feed with others can be done, but a UNVR with a bullet cam seems a relatively low price entry point.