Welcome,
and Yes they have, Sarnie is right [darn it, that makes it about twice now ]
500-800 depending on your choice of tyre all pretty much better than what Nissan put on to start with. I think a hat has an influence on mileage as well.
P1 seem to be 190 - 220 at the moment depends on where you are and of course if you supply your own oil it is less and you get better oil. About right for P3.
String I used today was 1.2m, but it can vary.
Modding can run up thousands ask around.
For insurance check out http://www.350z-uk.com/forum/viewtopic.php?t=10922
and
http://www.350z-uk.com/forum/viewforum.php?f=47
and damn damn damn Sarnie is right again that makes about 3 times.
Welcome and enjoy !
Oh check out the for Sale section on here