Some progress here.
I started with some experimental PCB, but I did not like it at all.
So I was thinking how to get it done.
I'm not an Engineer and I do not have any background in this direction, so I started reading and experimenting.
Never used Eagle CAD before ... so I had to learn this as well
I thought it might be helpful to etch my own PCB, so I played around with the Heat Toner Transfer Method, the Cold Transfer (Aceton), but I was not happy with the results.
Now the Board is painted black and used a laser to remove the details which I don't need in the final PCB so I can etch it.
In this design I'm using voltage divider to get the 12V inputs 'translated' to the 5V the arduino can take as an input, but I'm still not happy, so today I ordered a few Optocoupler ... let's see how this works
If somebody has input / hints, I'm listening.