second-hand vehicle financing, 5000 euro

hello, I finished my training last year, now work since november 2012 in a permanent job in another company. since I have to drive about 35km to work every day, I got a scrap box for 500 (opel corsa). that I need a new car sooner or later was clear. now I thought to finance a used car over a relatively short period of time. an audio a3 8P for approx. 7-8,000 euro. (year of construction 2003/2004, up to a maximum of 130000 km) I am 23 years old, earns approx. 1350 euro net in public service, indefinitely. I would have to deduct 200 euro from the net salary for petrol, so I still live at home no rent. I wanted to put away 400 euro for the car (for rate and maintenance), so I stayed about 5600 to live. until May I would have about 3000 euro together, which I could take as payment. so I would have to take still pimal daumen 5000 euro credit, which I then in a ze at the end of the year I get a special annual payment, about 80% of the salary in addition. I would also get back by the tax return also around 2500 euro, due to the travel costs to work. for me actually the reason that I would have paid the 5000 euro relatively quickly. I always wanted an audio and the dream I would like to fulfill now simply. about the financing you could argue about now, but I want to j not waiting another 1 year. what do you think about it? is that portable? did I miss anything?