try buying off a forum member as USUALLY it would be better maintained. its really upto you how you want to go about it. if you want to grow with your car and mod it to your taste then do that, or if you dont mind finishing off someones work then yeah haha.
personally, from experience i would buy a car modded already, as ive bought 2 stock skylines which ive spent a fair bit on both, if i was to buy another one id get one already done
at least get the basics, exhaust, suspension, fmic, air filter & ur off to a good start already.
oh and ive had a s2 gtst, its a realllly good car mate good choice