Wet nitrous setup means that a fuel solenoid is setup to spray fuel in conjunction with nitrous. It's easier to tune since you just have to follow the jetting size. Dry nitrous setup means only nitrous is sprayed, so the vehicle fuel parameters must be changed to be richer at WOT. It has nothing to do with the amount of hp going to the wheels or crank. Zex has a weird jetting system where a 125 shot is 135 at the crank but 110-115 at the wheels. NX typically follows the whp jet ratings.
A good bet is to begin with 75 shot wet kit, and step it up to 125 once you get used to it. The stuff you need are the proper spark plugs, 93 octane and correct spark timing retard (0 for 75). Other stuff that'd be highly recommended but aren't required are: RPM window switch, bottle heater, blow down, purge, sticky tires, and a fuel pressure-based cutoff sensor.