Ummm........20's at LARGEST....... It's a passenger car, not an SUV man. Shoot it's not even a E class Mercedes. In my humble opinion 19's are the largest I would go. Anything else is going to look way out of place. Don't be one of those guys that makes a car look hideous by doing something so far over the top that looks stupid.
Again, in my opinion, the best way to modify a car, is to work WITH the car. Putting a rim on a passenger car that is 4 inches larger than the largest size offered in stock form is ridiculous.