Just a couple of thoughts:
When I've played with RS485 in the past, I've started by sending a single ASCII character in upper case and programming each slave to respond to a specific ASCII character by changing the case of the character as a response. Once I was happy with that, then I expanded the functionality.
I'm pretty sure that the standard MAX485 modules (with the pin organisation as you have drawn) are 5V devices. These should be fine for your Nanos but I don't know about your ESP32. Is the ESP32 5V tolerant. There are other RS485 modules that use a transceiver that will operate at 3.3V.