hey Nacho, you definitely want to ask for a 20% tint. Radioactive man has a sedan with beige interior like yours and it looks sharp. It will look slightly lighter than mine since I have a black interior.
If you are going to run a minimum 18" wheel year round, the next time you do a brake job you can have your BMW dealer install the "BMW Performance" cross drilled rotors. They are larger and the smallest wheel that will fit over them is an 18, super sexy! I don't think there's a huge difference in the cost difference between stock and Performance rotors so if you do it when your stock's are worn out it'll be perfect.