If you want to do n2o right then get a wet kit (NX, compucar, dynotune are some good kits) (i would not get a zex because they do not put out as much power as others). You could start with a 75 shot and see if you are happy and still have room to grow. I am going with nitrous this spring and plan on running a 100 or 125 wet shot.
I dunno why you are limiting yourself to the sneaky pete. The only advantages i know of are the smaller hidden bottle and you get power from 9v batteries. So the only thing that is easier is you pry dont have to run power wires but anyone who knows anything about cars can do it.
If you do step up in shots to 100 then a fuel pump and adj regullator would be good things to add to the list along with the colder plugs gapped tighter and a tune.