My setup is simple, HA - Arduino - sensors.
There are a lot of techniques and names in this sphere, MQTT, Json, Firmata etc. Can someone tell me if I have any gain of these?
The normal setup is
HA - ESP Home device - sensor
If you want to use an Arduino then you'll probably need to create a custom sensor inside Home Assistant and use MQTT as the message layer.
Seems MQTT is not for my gear as it require TCP. Only 'vintage' stuff here. 
Thanks for your input!