In the previous entry I stated that I had no idea how to hold all the components together, and my original plan was to use some wiring to connect the POE module and Ethernet jack to the Pi and IR ring. But as I got more confident with my PCB layout skills I decided to put everything onto a single board, and create a Pi Hat.
After playing with component orientations for hours I think the assembly comes together quite nicely.
The Ethernet jack connects to the POE module which feeds the main 5V supply to both the Pi and the IR ring. The Ethernet data lines come out at a connector that will require feeding back into the Ethernet jack on Pi3. As a fun extra the Pi3 can drive each channel of an RGB status LED. I've attached an exploded view so you can see how the components fit.
(I will write more about the IR pass-through filter in a future log.)