Ok, I'm not trying to be rude or anything, but it drives me nuts when people call it a "nos zex kit" NOS, is a company, "nitrous oxide systems" Zex is a completely different company.

Anyway, Nitrous and boost works very well, but with a 16g you don't wanna run any more then say a 50shot. Nitrous will spool that turbo damn near instant as soon as you hit the nitrous (kinda like a supercharger effect) But after time the exhaust wheel is not going to like you very much as that turbo has an extremely small wheel.

2nd, if you are going to run the nitrous make damn sure you turn the boost down alot, the nitrous is going to spike that little turbo another 8-10lbs of boost when the nitrous comes on.

If you are serious about this then If I were you I would invest into some ARP head studs. The last thing you want to happen is to lift the head, stock head studs just suck. You may get away with them but not likely.

3rd, allways, and I mean ALLWAYS go by Zex's recommend jets sizes, don't use NOS or nitrous express's recommend jets. And allways when asking Zex about jetting sizes for the fuel and nitrous to tell them what car it is on, they will ask you what fuel pressure and what not.

I would recommend using a 30shot to begin with or a 20shot like you stated, then work up to 50 shot and maybe 75 shot if your brave enough.

Now, when tuning on the nitrous, allways start out at low bottle pressure IE: 850psi to start with. Then work your way up to 900-950psi, bottle pressure is the key here, too low of pressure and you will just run way too rich, too high of bottle pressure you run to lean and risk of blowing the motor. Nitrous is not very forgiving so keep tabs on bottle pressure at all times. With nitrous and turbo you want to shoot for a 10.8-11.0 A/F ratio. Nitrous makes enough power that runing rich the car will still make tons of power from the nitrous. Better rich then sorry.

And a rule of thumb with nitrous that I have allways followed, for every 50hp shot of nitrous you wanna pull 2 degrees of timing out. So if you are running 20 shot or a 30 shot then just pull 2 degrees out to be on the safe side of things. Make sure your fuel pressure regulator is up to par and make sure your fuel pump is enough to flow enough fuel for the nitrous and the injectors at a given psi.
But to be honest with you, on a bone stock motor with a 16g and nitrous you are asking for trouble as the rods will not like you as much. One small mistake on the nitrous and boom. But if you insist to use it then be carefull.
Nitrous has gotten a bad rep just for the fact that people go beyond the reccomended jet applications, bottle pressure ect ect. Allways hit it above 3500rpm, you can get away with hiting the nitrous at 3000rpm, but just be safe and don't risk it. Motors are detonation prone at low rpm. So allways hit it at higher RPM.
don't get too crazy with it, but if you use it, just remember, turn the boost way down before hiting the nitrous as it WILL spike like none other.

Good luck.