Everything works on the breadboard. I've tested everything a few times. I've even made sure everything fits inside the PVC. The only thing I'm missing at the moment is the voltage regulator that will allow me to power the ID-2 (among other things). Since the Pro Trinket can only output 150mA and the ID-2 needs 200mA the regulator is necessary.
While I've been waiting I've been experimenting with the PVC--seeing just what I can fit in there along with everything else. There's plenty of room! I also made an indentation in the pipe so that the OLED display doesn't get scratched when being placed face-down on a flat surface: