I get 430 - 450kms to a tank in the GTR. Stockish just catback exhaust and intercooler etc. Insurance is whatever your quoted. Oil change as mentioned every 5000ks which is about every 4 - 6 weeks for me.
It all depends how much you drive the car really. Servicing is a bit more often than a normal car and with higher quality materials that's all. When you start to break stuff it gets expensive lol