Hard to say really. In my experience this strongly depends on the retoucher who does the final artwork. Some retouchers demand different passes than others. But in the end, they all basically need Lighting, GI, Reflection, Refraction, Specular, sometimes SelfIllum. Other passes are optional. A friend of mine is freelancing as retoucher, he does crazy stuff using the raw reflection pass. He abuses it in my eyes, but hey, the results were nice 
Mostly dictated by the manufacturer. Mercedes had no problem with that back then, for Audi this is a no-no nowadays.
Modelled treads, but displaced sidewall details. I set the displacement to static, which renders quite quick. For spinning tyres, the displacement is disabled, because you can barely see it.
Often the photographer uses a stand in car on the set and can provide details like camera height, distance to front wheel center, lens etc. The perspective match tool does work very well, if you can find enough lines in the backplate. Also, there is the somewhat hidden camera match tool. Saved loads of work for me and is one of the things I can not find in Maya.
Never used it for cars. This is more common in architecture I think.
Mostly the car companies. Had the case where I needed to render the new M-Class for an ad campaign. The camera angles were set up and provided by the M-Class product manager of MB. The photographer had no influence on this.
Direct light. Reason is that you give a certain color to the direct lights. I then make three lights, one red, one blue, one green. Each with slightly different settings or position. I then render these with the raw shadow pass. This will result in colored shadows in that pass, which you can easily select in PS using the color channels. Basically a mask for each shadow…
Because I am working for print, I do not need these rigs. Only thing I do is make a little setup for spinning wheels and for steering. I need that for rendering them with motion blur. Some dataprep companies like RTT can provide groups and helpers for this, but in general this is all a big mess. In Max at least, because they do it for Maya.
Max ftw! I am the only one in my company who is using it, everyone else uses Maya. And to be honest, I can see no point in that. Everything seems to take ages in that software, even simple tasks are overly complicated. Also, Max has a whole lot of neat features out of the box which Maya does not have. Again, this is for print, not animation.