I got some stupid question to ask.

I just bought a 300C, and would like to buy a 20-22in wheel and also air suspension compressor for my car, but here's the question.

1st question: Do I need to do some work on the wheel arch? (I don't know what was that) as I saw alot of VIP car in japan had to do some fender work to allow the 'big' wheel 'suck' into the fender and camper...)

2nd question: Do I need wheel spacer for such big (20-22in) wheels?

3rd question: What is the difference between a 6 piston and a 4 piston Brembo brake?

Thanks, is my very 1st car and I really no idea what is what...thanks again