How variable are 3-way financings?

Hello dear people, I have a question about the “diversity” of a 3-way financing. Currently I am a student with a regulated smaller monthly income, which my company pays me (dual student) and drive one, through the factory leased, Audi A3. Now I notice more and more, leasing is not so right for me. It is great at my age always to drive new cars, because I get a new one every 8 months and also that I never thought about workshop costs However, a small screwdriver heart and full of envy I look at my friends, who can make all kinds of beautiful changes on their cars. Of course, I don’t like this possibility with the leasing vehicle, so more and more the desire in me cooks up to me to get my own vehicle. As a car enthusiast, of course, it should not be a bread and butter model. It should be sporty and fun. I actually think of GTI up to max. 18. Thousand Euro. The pity is only, I have no savings in order to be able to pay a fee and the monthly instalments should be quite small with 100-150€ (so that I still have enough reserves for maintenance etc.). My thought game was now: 0% down payment (possibly paying an old used one), small instalments (100-150 €) and then large closing rate. The big closing rate is no problem, since I, with a 36 month financing, in 18 months full working engineer I would also like to know whether it is possible to adjust the monthly instalments after e.g. 18 months from 100€ to e.g. 350€? I already thank you for the answers. Have you had a good evening yet! I would like to thank you for the answers, and I would like to thank you for the answers.