First car searched 500€ / month

Hello, I’m looking for my first car and I’m just going to write together what I’m so interested in. Maybe someone has a good idea. Brief history: I’ve only had company cars (Audi A3 Cabrio, Audi A6) or high-quality car rental cars so far and I’m pretty spoiled…. Now I’m looking for my own car: – driving performance approx. 15,000KM – 20,000KM / year (20km city traffic daily to work, the rest of the long distance) – budget incl tax, fuel, insurance max. 500€/month – It should be a used car – brands: Actually only Audi, BMW or VW comes into question. I love it at the moment with an A6 Avant, Bj 2007. It is available at Autoscout for about 20,000€ or a 3rd / 5th Touring. However, I also find a convertible very attractive. Is there a possibility to finance / lease a convertible and after 1-2 years (when the offspring comes) to a station wagon? My problem is also that I have no idea what a car a month of side food I’m 24 years old and I’ve had my driver’s license for 6 years. Probably the insurance for such an A6 isn’t just cheap or? As I said, that’s what I’m thinking right now. Does anyone have a few ideas? Thank you and many greetings