I dont get it.
First you claim you want something small and nippy, and now you want a BMW? IMO, go for something small like a corsa, clio, saxo etc to keep the running cost's down. In the BMW, you will be going through tyres alot faster than you would if you was in a FWD econo-box due to the rear wheels having drive, so you will wear them out alot quicker than you would on a FWD car.
Also, repair cost's would cost more and your insurance would be more expensive as would your fuel consumption.
Also, (and im not trying to be a troll) i know i have said this MANY times before on this thread, but your dreaming. DREAMING.
Stop day dreaming about what car you think you are gonna end up with, and concentrate on getting some actual money so you that you can go and buy this car when the time comes. Its all well and good getting advise about what car you should buy, but your getting too excited and ahead of yourself. Your not 17 until February next year, so it (in real world terms) wont be until april/may kinda time until you pass your test (maybe longer) and thats even if you purely concentrate on getting it done. Your going to need money for your lessons and tests with the lessons being expensive, so there going to cost you alot. Also, if i remember rightly, you dont even have a job yet right? Another reason why you should stop day dreaming and concentrate on being able to get everything you want as atm, all this talk about you wanting to buy this car, and do this modification to it is extremely pointless considering you have no sort of significant cash flow.
Again, i dont mean to sound like an arrogant prick, but its the truth and you need to realise that. Get a job and some money, then come back here instead of hopeful wishing.