I have just bought a 325i and oh my god its wonderful.
It is probably gonna be a bit expensive for you to insure as I have five yrs no claims and am 35 and its certainly more for me than my previous Honda but shop around Liverpool Victoria are generally quite competetive.
The mileage should not really concern you as BMW s go forever if they have been properly looked after but maybe you should consider something more practical for now after all it is your first car......
From experience they are worth the wait x