I've started by laying out the five boards in Eagle 9.52.  Boards are now being ordered through JLC.  All parts have been ordered through Mouser and Digikey - however sourcing a small meter and solar panel that will match have been a bit of a challenge, as there are no specs published.

I also did a layout of all the boards to make a laser-cut base out of wood.  Ultimately it will also have a box to hold the jumper wires.

Once all boards and parts are in I'll begin assembly!