Looks like Adafruit has done a lot of the work for me while I took a break from this project. The most time-consuming bits when I started out were fighting through getting the touchscreen to work with the camera, and it looks like they've wrapped all that up in a nice set of instructions here:
Finally the O/S support for the Pi camera has improved much, so now it looks like getting it to work is simply a setup option, sweet!
Based on all this I'm going to re-cobble my hardware and put together a software stack based on what's now available. Once that's done I'll be turning my attention to the parts of the software that are not off-the-shelf (handling the network transparently and the Forban configuration). I may also be able to pick up a second camera worth of hardware now that I have a convenient place to buy it all...
Hardware-wise the case and battery still need to be sorted out, so there's work to do. I also want to investigate some of the other tiny ARM platforms that have come out since I originally embarked on this project, as well as other types of devices that might participate in the network (storage-only nodes, mobile network uplinks, etc.)