Good words of wisdom. I forget not everyone tows with a 3/4 ton diesel and even a 2500 lbs load can push around an SUV tow rig.
Not a bad idea, but if the car is properly strapped, it shouldn't move at all.
I agree with your method for setting ball height and tongue weight.
I won't say what you're saying about strapping to the wheels is wrong, but it's certainly not the only "proper" way to do it. You will notice most of the tractor trailer car haulers strap(chain actually) down the chassis compressing the springs.
I tow a vehicle on a car trailer probably twice a month on average. I typically strap to the frame and compress the suspension to the bumpstops. Then add a backup strap to the rear axle just in case all hell breaks loose.
In the end, there are a million different ways to strap a car to a trailer, as long as you're using common sense and proper hardware, you will be fine.