Heh.. practice.

2 and 3 Mikey seems to have answered quite well. But I'll be a little more specific on #1.

practice practice practice.

LOL! Nah, j/k.

Basically, you just gotta figure out how fast your vehicle is moving in relation to the rotation of the tire. Set the animation for the vehicle first, then go in and set rotational values for the tire. Start low because if you put too high a value then the tire can actually look like it's spinning slowly (this has to do with the frame rate of your video card). work with a small section of animation and work up the rotational value until you get a clean, complete rotation. Then just set the same value for the other wheels, setting the opposite sides to negative, of course.