Bi-directional control NR - Arduino

Why are you even considering Modbus? Have you developed an affiliation for hexadecimal buffers since you posted that in another thread? :stuck_out_tongue_winking_eye:

That's an effective strategy.
Keep your logic in one place and just exchange commands and sensor readings with your remote devices.
Personally I use ESP32s rather than Arduinos, smaller, cheaper and with on-board networking.
There must be advantages to Arduino boards but I've not discovered them.