Replacement for 15-20t€ and just under 10t km/a

Hello dear community, the following situation: – dual student – weekly 6 days by train to the next larger city – journey to the station is 10km – current car: Opel Astra G with 150,000km and almost broken exhaust –> Tuv due in May – fuel consumption is 9 liters, mostly more 10l – Fridays is driven by car and Saturdays back –> 140km – nothing saved – duration of study: until mid 2019, after that already bound the next 2 years with the company – number e currently 600€ Insurance per year My question is this: 1. Is a loan paid by paying only the interest annually and, if you start working, the rest of it? 2. Would my insurance be cheaper in the year if I had a new car? 3. What do you think of it overall? Too high-risk because of your studies? 4. Which car would you suggest to me? Should it work towards Ford Fiesta ST, Seat Leon FR etc. I would like to thank you in advance! Greetings