I think the diagram is a good basepoint for the wiring, however how are you increasing the fuel pressure? In this system the fuel is provided from the stock rail which as we all know is fed from a regulator on the fuel pump, hence no return line.
What happens here is the fuel pressure varies in the feed line so by adding in a tee to tap off fuel, what you are getting is a varied fuel pressure, it varies a lot BTW. How are you going to balance the nitrous to fuel? As the nitrous is supplied at a constant pressure (well it should be
) the fuel varies and you get an imbalance meaning that you cannot match the jets correctly. You run a risk of running very lean or over rich, neither of which is that good for the engine or cat etc.
What I did on mine was first establish the pressure variance, this was done by fitting a fuel gaage onto the tee and going for a drive, big swings. The answer was to fit an inline regulator, drop the pressure to 10psi, which is well within the capability of the fuel system, and match jets from there.
The results were excellent, my original setup was supposed to be 50 shot, frankly I could have got more power with octane boost. With the regulator in place I got what felt like 50bhp more, probably not but definitely damn close.
As for whats the correct amount to run, my shop is an authorised NOS dealer, we never fit more than 50% of the stock engines power to an engine with stock internals. Beef up your innards and the gloves are off
Its also best on high shot system to fit a secondary fuel system purely for the nitrous side of things.
Also note that on any not FI car with an FPR and return line up front, you should really be fitting a dry kit, such as the NOS one, this has a pressure device which adjusts the FPR to give more pressure thereby matching the pressure to the nitrous feed, and it works very well indeed. Unfortunately with the G7 there is no such fuel system available so wet is the only way to go, treat it like an FI car and things should be fine.
As a side note, the setup on my G7 will be direct port, I will also be fitting a secondary fuel feed and return. My car is supercharged.