Mine came with HKS Iridium's when I imported it, I didn't know how old they were so I replaced them with standard NGK coppers, and have been doing so ever since. I much prefer the thought of using copper plugs and changing them regularly rather than dropping something in and leaving it. They cost 2/10th's of sweet FA anyway...but yeah, they're in a bitch of a spot Maybe I'll hold my plug changes out to at least 7,500-10,000km's then, 5,000km is probably too often for a fairly stock car.
I'm just so used to servicing the Pulsar every 3,000-5,000km's (read also everything is much easier to access) that I guess I translated that onto the Skyline when I bought it.
Fuel filter I really believe people don't do often enough. Take yours off, bang it on a table and have a look at the junk that comes out of it. That sludge can't be good for your injectors.
On the oil side of things - what's the recommended viscosity? I always wondered as I've been using 10W40.