This is a minor update, but I was able to get the Arduino IDE to compile the code successfully late last night. It was too late to try actually moving the code to hardware (and hardware isn't set up yet), but it was a nice milestone to pass.
For those who question my interest in compiling with the IDE vs. going deeper with avr-gcc and friends (such as myself), I counter that this is intended to be a lightweight project that's easy to use. Setting up the Arduino IDE is about as simple as they come. I want to get to the point of compiling with gcc and uploading with avrdude, but that's for later.
Up next: building up the hardware on a breadboard, and seeing if any of this stuff actually runs!