I would only go for the back windows, rear and 2 sides, as 70% light has to shine through the glass, and the 5 0 carry gizmos to check for this. If you go ahead with window tint, I would check with your insurance company as the car is being modified from the original spec before carrying out mod, as the premium might go up, if they say it makes no difference, get that in writing, as if any accident did occur, they might try and wriggle out of it. Beemers will always be target cars for thieves, having a film of tint would not stop them, they would just bend the window frame on the door back to gain access. with windows tinted you are more likely to be stopped by 5 0, if you do get it done go to a decent window tinting place, search on the web and look for reviews, cheapest way is to buy the window tint kit, but if you go wrong could work out dearer than having it done by professional shop. Good Luck