Updated 8/21/2019:
Regarding the power distribution panel, I plan to move the working TPC-400 to District 1 (the River Route). That will eliminate wiring changes to that area of the board. And it will allow me to switch between Conventional (for the kids' and non-command equipped trains) and Command using the CAB-1. Districts 6, 7, and 8 will get new Legacy Powermasters, which will be set to Command mode via the slider switch.
That looks like a win-win scenario to me.
More when I know it.
George