What school do you go to? I am a designer at Ford and teach at CCS.
I looked at your sketches and briefly read some of the responses.
To become a car designer, you need to separate the design part from the drawing part. If you're learning how to draw while you're trying to design, trying to communicate the car in 3D actually overtakes the design process.
You seem to have a good handle on proportion, but your perspectives are a bit tricky. I would suggest developing the design in side view first, to get the overall proportion of the car right. Then do a direct front end view and a direct rear view. This way, you'll understand your design before trying to draw it in perspective. Now you can use the rules of perspective to communicate the design in 3D.
I gotta run and do errands, but I will let you know more later....