Congrats OP!
Im 16 and payed 14.5k of my own money for my car (it was 30.4k, i was supposed to pay half but my grandfather pitched in the extra thousand or so). Other family members got used cars for free. I decided i wanted to work and have a nice car, so i worked 4 jobs (3 part-time, 1 full-time during summer. These included Publix, Lawn service, assistant for a stock broker, and cleaning warehouses for my dads business) and still managed to get A's an B's in AP/honors.
I hear people say they "paid for half their car" when in reality they saved up maybe 2k or less. Makes me sick when i had to work so hard to legitimately pay for half of it.
As others have said, dont skimp out on "saving" money on mods. Get what makes your heart thump
Glad to see another young guy working for their car. Try to do the maintenance yourself (well, everything that doesnt require lots of skill/machines/expensive tools). I know i have been trying to, and it makes you more confident with your vehicle. I know i was, especially with a relatively "fragile" car like the 335i.
Anywho, my post is WAAYYY too long and im sorry,
IN SHORT: Congrats!