My current pin configuration looks like this:

I have 3 external boards:

Muliplex: TCA9548A 2 Distance Senors: vl6180x 1 Raspberry Pi

The TCA9548A has 4 connections to the Pi:

VIN -> Pin 2 GND -> Pin 6 SDA -> BCM 2 SCL -> BCM 3

The vl6180x have 2 connections each to the Pi: Board 0: VIN -> Pin 1 GND -> Pin 9 SDA -> SD0 (multiplex) SCL -> SC0 (multiplex)

Board 1: VIN -> Pin 17 GND -> Pin 25 SDA -> SD1 (multiplex) SCL -> SC1 (multiplex)

In addition, I have a hookup to an L298.

Red -> BCM 13 for the PWM Grey -> BCM 26 Black -> Pin 39

The motor hookup for right being forward is Black on top and Red on the bottom.