Next, tested each switch. The all work! Red wires are all connected to 5V supply and green wires are brought to 5V when a limit is hit. Each pair of switches has its own port on the board, so the computer will know which axis has hit the limit - but not which switch. When a switch is triggered, the CNC routine will stop.
Usually, with this many wires and connections, I find I did something wrong. This is worth celebrating.