The CVT gearbox is about $1k and genuine Nissan oil from Nissan is the only way to go. DO NOT service the CVT yourself, unless you are extremely mechanically competent, but sadly there ar eonly a handful of workshops in Australia with any idea about the CVT gearbox at all.
Sadly I think the guy was pulling your leg about a loose ground wire - and if it was that easy to fix, why didn't he fix it before he sold you the car?
The high beam/fog lamp is a H4 dual filament. You will never find a high beam light anywhere near the whiteness or intensity of your low beams, as the low beams are HID. The closest you will find is the Phillips X-Treme Vision, but even they are yellow in comparison to your HIDs.
http://www.ebay.com.au/itm/1-x-PAIR-Philips-H4-Headlight-Globes-X-treme-Vision-100-Brightest-Upgrade-EVER-/140747389599?pt=AU_Car_Parts_Accessories&hash=item20c532ba9f
Your bible of all things V35 sedan is here:
http://g35driver.com/forums/g35-sedan-v35-2003-06-15/
Every single thing in the world you could ever think of has been covered in the G35 forums!