I remember seeing an old set of asbestos pads for R31s back in the day (mid 90's). They perform awesomely but obviously kill you with the dust.
I didn't know they were banned to late here.
OP, get parts yourself and ask/pay your neighbour to help out. It's more fun working on your car and using logic/Google to fix things rather than paying someone. Takes more time though.
Brakes are easy as though. Just make sure you bleed your brakes as well.
Although $550 is a good price for new rotors and pads fitted, you need to know what brands are used.
As for pads, I think TRW make a good pad that isn't dusty, or maybe this new Intima pads. I used QFM HPX and A1RM, they are dusty but do the job well.
The reservior in the boot is for ATTESA not HICAS. Also the G sensor isn't used by HICAS AFAIK (R32 remember).
Most likely the computer under the boot. Unplug the smaller plug (there are two) and see how you go. The computer is located on the driver's side, under the parcel shelf.
The manual steps to invoke the diag mode is a pain, it took me a few tries to get it working.
1. Learn how to construct sentences properly. It will help you in life.
2. You don't have basic understanding of how a turbocharged engine's components work together. This means you'll have to research them yourself in your time. No one here will school you in that, so have fun Googling.
3. Sell your after market blow-off valve and spend the money elsewhere (e.g. better tyres).
4. Look in the DIY section for grounding the standard boost solenoid.
OR, ignore everything I said and do whatever you want, because it's your money and your car.
You'll need to think up a voltage divider circuit for the park lights.
Or... Two circuits connecting the LEDs (depending on how you want the lights arranged), one circuit connecting to park and the other to the brake wiring. Not sure what voltages are outputted (you can easily measure those), but a crude way of wiring them up... pretty much what r31slpr posted.
After some diodes and resistors, the lights should get e.g. 5V for park and 12V for brake.
The protoype is doing the rounds.
http://www.autocar.co.uk/car-review/infiniti/q50/first-drives/infiniti-q50-eau-rouge-prototype-first-drive-review
http://www.autoexpress.co.uk/infiniti/q50/87922/infiniti-q50-eau-rouge-concept-review
http://driving.ca/infiniti/q50/reviews/road-test/car-review-infiniti-eau-rouge-could-be-the-best-sports-sedan-yet
Yeah it seems like it's undercutting the Germans, but then this is essentially a V36 Skyline coupe so it might be getting a little old. Doubt the interior fit and finish would be the same as a new German coupe though (judging from some reviews that I read of this car).
Still, for $70k it seems like a good buy compared to what else is available at that price. An equivelant-powered German coupe is $100k+.
But for $70k, I'd be looking at the Q50 Hybrid.
From the UK and USA:
Q60 COUPE
FROM £36,780
Starting at $40,950
Plus taxes + rego
But they are putting the Z34 under the pump, if they're still selling those.
FYI 370Z price in the USA/UK: $29,990/£27,015
Wait until you are off your P's and buy a factory turbo car.
Don't bother wasting money on "performance" mods you listed, most of them are useless. Standard cooling setup with clutch fan will be fine, only upgrade to thicker radiator if you can rule out everything else.
Suspension = leave standard if you're travelling on tough roads. Bilstein + springs would be the go if you want to upgrade.
Brakes = full flush, replace fluid with high temp Super DOT4, good pads and rotors.