Hi, Joe
As for the body movement in your question, since I am a newbie and just learn this tutorial, I don't know the best solution. But your question is good and interesting, I spent over one hour to think about it. In reality, the body will be pushed upward and tilted by the pistons on the four corners. It is hard to simulate it in blender I think. But for a compromise, you can apply four transform constraint to the body (to make the z value of the body is the average of the four pistons or tires), the target of each constraint is one piston or tire, and set the influence of each constraint to 1/4. But I hope there will be a better solution :)