I would say take all your lenses. You might find that the 50mm is a bit limiting with moving shots, you'll probably want the ability to zoom in and out. 50mm won't be wide enough when the cars are close to each other on the road.
Besides f1.2 won't be any use when your subject is moving so much, the car will drift in and out of your depth of field.
Best idea is to try both the 18-55 kit lens and the 50mm on the journey and see which works for you.
With the rolling shots, you want to pick a shutter speed that isn't too fast that it freezed the car AND background, because then it'll lose any sense of speed, but you want a shutter speed that captures the car but allows the background to blur a bit. Start at something like 1/60th and see how that looks.
As for ISO and settings: you can't plan for sunlight. You'll have to get used to changing ISO according to what light is falling on your chosen subject. Even on a cloudy day, you can still have lots of light, so you could still be able to have the ISO at 100, but pick an ISO to start with and work from there.
Remember the exposure triangle: if you up the ISO from say 100 to 400, you'll have to increase the shutter speed to maintain the same aperture (and thus depth of field). And if there isn't enough light at ISO 100 to give you the shutter speed and aperture you want, this is when you up the ISO.
Exposure TriangleWhich mode to use:
* if the subject is moving (cars, water, people) use Shutter Priority (Tv on canon)
* if the subject isn't moving, use Av because you'll be able to get creative with depth of field.
You don't *need* to use the lowest f-stop (f1.8 or less) to get a shallow depth of field, you can still get a good depth of field with f4.
Also don't forget to try different angles, for example crouching will give you a better view. Like this:
Jaguar E-Type V12 by
AlistairBeavis, on Flickr
This ^ was also at f4.
Above all, have fun, try things out.
