Hey mate, I bought my C34 from Nagoya, although it had been traded in by someone else rather than being imported. They were pretty good, although they did say it was being sold with a 3 year warranty, and then once the sale papers had been signed, they suddenly never offered a warranty on traded in vehicles . . .
My old man also bought a V35 sedan from them, and he has had no problems with it.
I'm pretty sure tyres will be changed at compliance, they wont be terrible tyres, but they wont be the best top of the line either.
For fuel, try to always run premium unleaded (98 octane), or if you really have to use normal unleaded with some octane booster.
I think Just Jap does servicing, but I may be wrong. I plan to take my stag to Autosport in Kirrawee for my rego check and a service.
Most imports have had their clocks wound back, check the seats and steering wheel for excessive wear, if it is fairly worn then the car has done a bit more than 52k km's. Sometimes the cars will have jap servicing stickers on them as well, which will say the km's and date of the last service.