Project Vienna. How was it done?

At the beginning I’d like to point out that this is just one of my research projects which is used to explore some completely different styles that I’ll use at my future projects. I know it has some flaws.
The current photo is my most advanced composite photo, made of  four different photos. The different photos I used are for the background, clouds, car and the female model.
The idea was to make a virtual world that you don’t find in reality. It wasn’t my idea to make something real but more something with an epic proportions. This is the line I’d like to continue in the future.
I had several influences and goals I tried to achieve, but didn’t copy them. One of them was Drew Gardner and his Winter Storms I think this guy is really good. The other influence was Jon Paul. He makes amazing photos that look very close to paintings and I really liked them for years.
What I did was to get a photo of the Austrian parliament in Vienna. It was quite a touristic snapshot. I cleaned it of all those electric wires, pylons, various statues, tourists, fences, etc. just to avoid having to many objects on a photo.
Then I added the new clouds that I took behind our house during a storm. I also added a layer of computer generated fog and mist. This is important because without it the background would distract the viewer’s view from the main objects. Without the fog it would all look like an snapshot that anyone can do.

I set this layer that the main objects have 20% of fog and mist, but the background 80%.
The next thing was the car. The car was actually a 1:18 scale model of a German Horch 855 built 1939 I bought on ebay. Horch cars were considered more advanced and superior to those being then built by Mercedes before WWII. Unfortunately their production plant fell into the Russian occupation after the war.
I took a macro photo of that model at my studio using one big soft box and a white reflector. Because the car model was about one foot long it was easier to make a controlled lighting. Thanks to my macro lens from Canon (100mm f2.8 IS) the photo of the model was practically razor sharp. I pasted it onto one layer in Photoshop, draw the shadows and that was about it.
The last layer was the female model. I took this photo in my studio also, cut her out of the studio background and pasted to one of the top layers of my photo.