It really depends on what you are going to use the car for....like if you want it animated or not, exploded or not, etc. If you are just looking for one view from the outside, then just focus on modeling the exterior of the car.
You can use anything or start off with any polygons, nurbs, subdivision etc. It won't matter if you model part by part, as long as you are satisfy with the outcome. If you do a good job modeling, you shouldn't be able to see much or any differences whether if you have used polygons, nurbs, sub, or all.
9 months into Maya...and still learning...
0 experience with any other 3D programs