maybe a different approach:Pic of my original Nano driven replacement just prior to install - it's a bit Heath Robinson:
1) each display unit consists of a small mcu driving a display;
2) the display units act as slaves taken data input from a master and visualize it on the display;
3) a master collects take from obd2 and user inputs and sends the data to the display units where the visualization is handled locally.
This approach allows scalability and modulization: the display units should be highly similar to each other, and the communication will be quite simple to handle, potentially via uart or i2c, or whatever suits your environment.