If I’m understanding what you are trying to do then yes that’s all you need to do.
In terms of the arudino sketch the only thing you need is to add the libraries mentioned in the blog and change the pins if you are using an esp32. You also need to add your WiFi details and mqtt server but that’s it with the sketch.
Once you have that up and running you can use node red to send the ble temperature to opentherm-thermostat/current-temperature/set
There are a few people trying to implement opentherm via esphome and there is a working example using the diyless board if you are more comfortable with esphome but at the same time it is early days.
@shcherban would you be happy to share the sketch you are using? I’m also lacking in the code department and I’d like to implement the full shutdown into the code. Or maybe it could be add to the github source but commented out to allow people to implement if they choose to do so. Sorry for being a pest.