I agree with Kent. Stop trying to over think and engineer the kit and the use of it,start with a known setup(the 18hp kit) test it and go race. I'm not a nitrous guru but I used to use it on my talon I used to drag race. As for the tune up I would use your box and pull the timing down a degree or two, jet the n20 so it runs a lot richer than you have been ruining(I don't know na numbers but I would guess somewhere in the high 12 to 1 afr), as good a gas as you can run per the rules, maybe a colder plug(non-projected tip), and last but not least I would start spaying it in 3rd or 4th gear.
All right you motor bike guys it's time to pick apart what I said to see if I'm even close on a bike.
Mike Reichen