sad as it is, id say save for a mortgage lol, mayb refinance ur loan in a year or 2 to get the 20k+ to get the 34, i bought my R34 last year... im now 21... so i was 20 when i bought it, and yes, i have a loan, its not the best situation to be in but when you really want something sometimes u do stupid shit... ie take out a loan, i dont regret it though because i get enjoyment out of it every day... anyhow
mileage is quite good, i couldnt give you an exact l/km as i havent calculated it myself, but this also depends on how heavy your foot is.
they are an awesome car, that said if you can hold off, investment wise, a home is a good choice (go the 34) lol
good luck wit ur decision