You need to check with the nitrous system maker how much nitrous/fuel the solenoids can deliver.
I'd forget the .8 sec delay and bring the nitrous in off the line. The 4.56 gears should be plenty.
My buddies car has only one system and he hits it with 500 hp off the line. He runs 4.56 gears too because his car is real heavy and we run quarter miles here. His 10lb bottle lasts the whole run no probs.
I run two systems so launch with a little less and hit it with the second system at .4 - .8 secs. I run 4.10 gears in a MW 9.5" diff. 40 spline gundrilled axles. I run a glide too with a 4500 stall Neal Chance aluminum converter. A lot of money but worth it.
You wanna make sure your rear end can handle a beating. I blew a 9" MW diff apart last season. You'll be needing a good trans cooler too.