you'll get different opinions on here, but insurance is worth it. If u write the car off, it's a lot of money to throw away if u dont have it! And it should only get cheaper as you build up a good NCB.Reliability is very good as long as you keep up proper servicing. Skylines are an awesome build quality compared to lots of aussie cars...you dont hear many stories about things breaking for no reason.
Driveability...they are seriously such an easy and comfortable car to drive. You can drive around town under boost or very low boost...the clutch is light and easy...you'll have no dramas. Just be careful when u decide to put your foot down, or in the wet, especially if you're not used to RWD!
As for kms, try to ignore them as most are crap anyway...you're better of looking at the wear and general condition, and get a proper inspection done by someone who knows their stuff..
hope that's helped!