How to organize talking between ESP8266 and Arduino UNO, that connected with UART?
well, I did something like that with an ESP8266 having a RFID reader attached, with send the data over UART to an ESP32. I just used the MJS UART example from the example apps and started from there - worked fine for me. To have more stable data transfer I would rewrite this in C, but as it was a POC, it was fine. The main problem to look into - be sure that there are no interferences with multipurpose GPIO settings.