I am using a Lorex NVR and a mix of Speco and Lorex cameras. As the Speco cameras fail I am replacing with Lorex.
I use 6 cameras, two on each side and two on the top. The two on the top are mounted so that one picks up the front of the car and the second picks up the back of the car. If you can get the side cameras mounted farther from the car (5-6') you can probably get away with one on each side. Mine are closer to the car and I angle them a little, one towards the front and one towards the back.
You can't have two many angles and they have paid for themselves a bunch of times. Maybe the best money I have spent in car washing. I have been able to resolve so many potential issues with a simple check of the cameras.
This is the Lorex camera I am using LNE8950ABW (currently out of stock)
This is the Lorex NVR I am using N881A63B-W
David