I'm close to having enough modules working to begin putting the pieces together and seeing some basic functionality. I need a control unit and a clock. Here I'm building a clock specifically designed for development - it supports extremely low clock frequencies (single Hz) as well as a manual clock button. I stole the basic design for this clock from Ben Eater. I made a few optimizations, namely switching the clock-select signal debouncer from a timer 555 design to a pair of NAND gates. I also used NAND gates instead of the combination of various gates Ben used - this way I was able to get away with two 74HC132 quad NANDs for debouncing + clock selection rather than the four chip solution Ben landed on. Here's the circuit:

Here's a photo of the finished board:

I tested it and it's working as intended.