First car

Hello together although I only start my driver’s license in the summer I have dealt with the topic. Currently I am 16 and would like to buy my first car in the summer 2019 when I have become 18. I have about 350€ available. I would have thought to a golf (Gti)(adventure? in the insurance/tax?) or a Bmw 3er best with M-package. Since I have no ideas what further costs will come to me and how high these will be. Ask me? How much do I have to do as a Fa hranfänger with the tax and insurance reckon what still happens? Since I am already finished with 17 and will make accompanied driving it will also be cheaper or? I make a teacher to the car mechatronicker. Smaller things I can do already on the car. I am also a big fan of tuning. However, I have no experience there and would then try with the car and screw something. Thank you for your answers and your help.