Firmata is a great communication protocol to turn a cheap ($5) Arduino NANO clone into a useful tool for home automation with 1 minute work.
Start Arduino IDE > load StandardFirmata example > click upload > FINISH, and you have:
12 port digital I/O,
an I2C bus,
connecting easily with a Plug&Play USB or an Ethernet port!
I haven’t found ANY other protocol so popular and with so many client libraries.
I use several ESP8266 devices in my home and they have lasted for over 2 years. If one goes bad I will just reflash a new one and be back up and running quick. Also, if your good with a soldering iron you can buy the esp chip and solder it to a dev board yourself. Doing it this way the cost is approx $3 US per device.
If you prefer wired it’s your setup but I find wireless easy and less clutter.
Use the mqtt binding but install mosquitto broker not the embedded one on OH as it’s no longer supported. Mosquitto can be installed using openhabian-config tool. If you do not have openhabian-config it can be added to any Linux based system. Here is a link for adding it:
The tool is very helpful and I recommend installing it regardless of what route/binding you decided on.
Another post in the forum you may find a good read.