@Yogurt_Man, thank you for the detailed reply. I have now distributed my three XL430’s on three ports and they are working fine (using BulkWrite() btw.).
With regard to sharing, I would be more than happy to do so when I’m finished, but there is one hurdle left I have to approach:
Since the Dynamixel rotates the thruster but the motor powering the thruster is controlled by a traditional R/C type ESC, I need to provide a PWM signal to the ESC. I plan for using the Adafruit PCA9685 via the OpenCM’s I2C port to keep servo connections simple (on the Adafruit board the servo connectors a neatly arranged).
The PCA9685 library seems to be compatible with the OpenCM 9.04 board (at least I was able to compile and run) I only have to solder the headers to the OpenCM to connect both. Since I am not the greatest solderer on earth, a task I have reserved for the weekend… 
I used the PCA9685 board on several other projects (with Arduinos, Raspberries, Jetson Nanos) and it’s a nifty little device, e.g. it can draw the power for moving servos directly from a connected BEC-equipped ESC, like in pure R/C setups.