I hope you dont mind me posting this in your thread. Coming to the layering thing, well yes you are right that every modification that you add goes on to a new layer and that the original look of car can be restored at any time during the work.
The selected layer (background layer) is the one which has the original look of the car while as the other layers contain different parts such as the FMIC, Eye Lids etc.
Now if i hide all the layers except the background layer, i can again view the original look of the car.
You can also merge all the other layers into just one background layer by pressing Ctrl+Shift+E.