You can tint front windows somewhat, but not by loads. For you, you want a car that's 1.0 to 1.2. These are the smaller engines, and so are cheaper to buy petrol for, and to insure. Any car will go plenty fast enough if the mood strikes you. Leave it standard. Be happy you've got a car to lug your bike around in. Sound system is a fair idea though, you can swap that out to the next car if need be.