Yes the two power pins can supply the complete module, I am using 12V for the ones I have which will also power a LoRa module.
As already answered yes it is automatic, just transmit the data and it is sent out, I am using a Modbus protocol based on one of the Arduino Libraries but it needed a lot of changing to make it compatible with the M5Stack. Works with some Smart Meters I am working with running on the second core of the ESP32 with WiFi and Screen handling on the main Arduino core.
You need to make sure you connect all ten connections between the sub board and the main board, there were no instructions with my units so I had to figure them all out. A, B, C and D next to the connector, 5V and GND to the top left of the connector, Vin T2 and R2 on the left side of the main M5Stack connector and if you want to use the current measurement you need to connect pin34 on the right hand side of the main connector. I found the easiest way was to use 0.1" pitch pins and solder them to the small board first and then the main board.
The current measurement is done by the other chip on the small board, it appears to be the current flow into the whole system if the unit is powered from the external power connections marked 24V and G