This is the reason that every single car built have "two eyes" and "four legs". They could have one, or three or five. A car designed by insects would have six wheels, but then people would reject the model as ugly. All cars have an upfront and a posterior "face". And this face depicts either a mammal or a person. Never a bird or a snail.
As for headlights, a single central one would still be notably face-like given widely spaced turning indicators. And having two headlights gives redundancy: "one-eyed monsters" at night are preferable to cars lacking any lights.
I doubt this. There are physics issues involved with 6 wheels.
First off, where are those extra wheels going? Dually pickup trucks exist, but that's just so they can carry heavy loads.
If you put them anywhere other than close to the existing tires, unless you attach some sort of steering mechanism, or perhaps use casters, turning becomes a huge problem as those tires would have to skid.
No, we use 4 tires because it's the most stable and efficient number of tires to use unless you need to carry a ton of extra weight.