Hey @bestes and @akers.kenneth66.
This is what I archived so far with the tutorial posted above:
- I connected my arduino to my raspberry and I managed to add it to Cayenne.
- Also connected a DHT11 Sensor and now I can keep track of Temperature and Humidity using Virtual Pins
([Dashboard values don't update] (Dashboard values don't update) thanks to @ats1080s ) - After that I hooked another arduino, edited the file cayenne-ser.sh to look for this second arduino and run another instance of the script.
Guess what… I have now two arduinos connected to the Raspberry PI and both can be controlled using Cayenne!!! 
Here is a picture of what I changed in the cayenne-ser.sh script to manage to have multiple arduinos connected to the raspberry.
You just need to change /dev/tty to the usb port.
I will post my entire project once I finish it for sure.
BR