The front air hole

As you see in the images below I sliced the front and made sure after mesh smooth the front where the windshield come later, was funded. Then I hidden the rest of the car to have more liberty working with the front. Basically I deleted the central faces and extruded the edges several times.

This is how it looked after the extrusions:

Next I lifted the edges in the upper part (the ones with red). After the edges were perfectly aligned with the faces (where the windshield will go) I welded the vertices (in the third images).

The lower part of the car (in front):

the air hole : I sliced all the faces horizontally and then I selected the middle face and I sliced them vertically:

Then I deleted those faces and extruded the edges inside, twice:

below you can see how I created the little bumpers:

The side airhole:

I only worked with one side of the car, then after I completed the airhole, I copied and mirror those faces and them I welded to the other side of the car.

I extruded inside the faces, twice:

After this part looks good I copped the faces and mirror them.

Now the work with this mesh is almost over, I wanted to be sure that the wheels will fit good in their holes:

Next :

After I applied mesh smooth :