Never heard of an Isuzu with nitrous, should be pretty sweet. I've had nitrous on my past few cars (Nissan 300zx, AP1 Honda S2000) and it was awesome, although there are quite a few things you should do for safety before spraying.

I do see you're going to be using a wet shot, that's a good first step. The other things i'd invest in before spraying is a purge system, a WOT switch, a window switch, and a wideband. On your VX since you will be using the stock fuel system I wouldn't go above a 50 shot for safety reasons.

The purge system will the clear the line and get the nitrous up to the solenoid ready to spray, if you don't do this you can have a delay in your system and you will run super rich since the fuel is injecting, but the nitrous isn't for a certain amount of time. The WOT (wide open throttle) switch is exactly what it sounds like, it's a little micro switch that is depressed as soon as you floor your rig and will activate the system. You should never use nitrous without giving it full throttle so this will turn on/off the system when appropriate. The window switch will let you choose what RPM you want the system to engage and disengage at, for example you really don't want nitrous spraying below 2000 RPM, so set it say at 3000 up until say 5500 RPM and then it will shut off so it can shift smoothly and won't have any AFR problems while doing so. Lastly one thing you don't want to skip is a wideband to monitor your AFR's, don't get one of those cheap crappy narrowband gauges (little light going back and forth on the gauge) they don't work well and are pretty much worthless. Get a Nice wideband with a seperate o2 sensor and have a bung welded into your exhaust so you can see exactly what your AFR's are at all times, this could save your motors butt if your running way to lean or rich.

If you have any other questions about nitrous stuff let me know and I can help. I'm assuming you already know what you're doing, but another persons insight always helps haha.

BTW, for nitrous a standalone will ALWAYS be better since you can get it tuned specifically for your vehicle. It's just very costly to do it the right way and to have it tuned professionally on a dyno. If you do end up getting a standalone be sure to upgrade your fuel system also.

Cheers and good luck!