nis0 the best thing to do would be to have somebody that knows GTR's to have a look. Paul has a great suggestion. post up where abouts you live and see if anybody from the forum lives near you. i'm out the south east melb and would be quite happy to look at a couple with ya. in the 1st year of owning my car i spend around 10k and the 2nd year another 20k. They arnt cheap to buy but they are more expensive to own.
As for insurance, with just car you can increase your excess to lower your cover. not recommended if you dont have much experience as for example, if i crash and its my fault, $500 excess + $1500 for a plus vehicle + the 'ad-just' excess (lowers my premium) $1100. =$3100 if my car gets stolen, even though its fitted with a kickarse alarm and immobiliser you can add another $1000 to that so =$4100. I am over 25 so i get to save on my age excess which i think is around $500 or $600 more.
The adjust excess is an option you dont hafta take but it knocked 500 off my yearly insurance and i do tent to drive like an old man when im on the road.
my 2c, if you can only afford the 20k you got from the bank, and really want a skyline, get something under 15k cos your gonna need that spare cash up your sleeve.