NX has very good kits. I dont know how far you are gonna take this but a single fogger would work fine up to about a 50 shot (over a direct port). Anything more than that you are going to need to beef up the internals. Many people also highly recommend a digital window switch, a fuel pressure safety switch, a nitrous pressure gauge, an EGT gauge, a purge kit, a blow down tube. While all that is not needed it is nice to know your engine is safe from most everything possible.
*As far as 2 purge valves goes i dont see the point. Unless you are going for pure show you are just shooting off more N20 into there air which is just wasting money.