4. Have every polygon detached to a different object, then rotate them and place them in the right positions. When rotating and moving the blueprint objects, you should take advantage of having the top and side views already aligned for you, by rotating the side view blueprint, for example in the Y axis, and not moving it in a way that will change its alignment. By the way, also make sure that the blueprint objects have Backface Cull selected in the object properties (Fig04).
5. After you have all the blueprints you can check if they are placed correctly by placing temporary reference objects in unique places on the blueprints, or by moving the blueprints interactively and having them intersect and seeing if all the lines match as they should (Fig05).
6. Now, after you have all the blueprints set in the way you want, disable Show Frozen in Gray, in the object properties, and freeze them (Fig06).
7. Before we start modelling straight away, I would like to share a method I've been using for a while now. I usually draw a quick and simple wireframe on an image with a camera angle that shows a good view of the car. I don't follow this wireframe precisely, but it helps me to better understand the form and plan what I will do before I start building all the edge loops.
Drawing a wireframe doesn't mean just quickly putting arbitrary lines on the picture, you have to think carefully how the edge loops will behave and keep it simple so that you can read it easily (Fig07).
8. After you have this image, just keep looking at it and at the reference images, then finally start modelling with the blueprints, keeping the wireframe that you are aiming for in mind.
When modelling cars, a lot of time I use spline modelling. Since I have the wireframe planned it appears easier to use spline modelling, but it's exactly the same as starting with a polygon and extruding the edges, so I am just going to do that so that it becomes less confusing, in case anyone isn't familiar with spline modelling.