I'd definitely put the nitrous kit on the new motor. Your new motor won't have any problems handling the 5115 kit. 10:1 compression & o-ringed head gaskets...I'd say your motor is begging for some laughing gas.
But you didn't mention what shot you plan on running? If you're using a 75-100hp. shot then the 155lph intank pump will be sufficient. But anything above 100hp, like a 125-150shot...you'll definitely need an additional inline pump (like a T-Rex or something similar) to help boost the volume of your fuel system. I use the 5115 kit, which by the way should already be equipped with the Hobbs fuel pressure safety switch that shuts off the flow of nitrous into the motor if the fuel pressure drops too low. I too have a fairly new motor that I had built a few years ago. I use the 5115 kit with 150hp. shot jetting. I have a 155lph intank pump and an MSD 200gph inline pump. The system works great. It knocks more than a second off of my 1/4 mile times, on motor. The kit is pretty full proof as long as that safety switch is hooked up. Good luck.