> How many deaths has Tesla prevented, which would have happened otherwise?

Certainly a larger number than the number of deaths caused by Autopilot failure (which makes major news in every individual case). Have a look at YouTube for videos of Teslas automatically avoiding crashes.

I don't see a number.

Yup, we used 4 wires for data and 4 for power - there's a 12V supply which is spread around and downregulated to 5V on each board. We picked ethernet because it's extremely cheap, hard-wearing, widely available and has enough wires to play with.