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In order. . .no, yes and sort of.
The area under the car doesn't count towards frontal area. The tires should count, but I wouldn't put it past manufacturers not to, and I might have useful info but most likely not.
The problem with any object is its amount of surface area. A long car will have a higher Cd than a short car of the exact same shape. Drag happens not only as it comes across the front of the car but as its pushed aside and "drag"ged along with the car. That part is what I call concurrent drag, or the drag running along the side, literally.
So if you can decrease the amount of air you have to accelerate(in a vacuum you travel faster) it costs less. If you lower the car it makes it more difficult for the air to get under the car. If there is less air underneath the car then each molecule of air the car does accelerate is not immediately decelerated by as many surrounding molecules.
Lowering the car is like creating a greater vacuum under the car. less air less friction.
Skinny tires provide less frontal area.
An example if you have ever ridden on a train and had your head by the window as you and another train cross paths it hurts your ears. I traveled on the Eurostar and when we passed another train headed the opposite direction only inches away the pressure change would hurt your ears until it passed.
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