So long as your nitrous kit is a wet system, you can use a slightly larger jet for the fuel, this should enrich it enough that you won't get any detonation, don't go too big on the jet, or you will need to worry about bogging or fuel puddling. Once again, try to run at least 93 octane like many others have recommended. Wet Kit's are safer imho, and are less likely to cause detonation in the first place. Seeing you run an automatic, you will have an eaisier time running a wet kit anyways, since fuel management options are limited.
PowerFC should work on an auto, with the right program and harness. Brash Boy sells PowerFC systems for the auto GTS, so that's a good starting point. Also may want to look at split second for your fuel management needs.
Alcohol or water injection may be another option for you, but it's not for everyone, still, it's an option.
The mallory switch is cool, just make sure you dial it in properly, a switch that uses pills is a little more accurate and safer. if you go with the mallory, make sure it's installed in a place where the knob can't get jostled out of place, or put a piece of tape over the knob once it's dialed in so it's setting doesn't get out of whack. This is if it uses a dial or knob for setting the trigger RPM, some units use jumpers or dip-switches instead, which is way better in terms of control/safety.
Oh, and that lag when you first launch is pretty much something you need to deal with. Try rolling into the throttle instead of mashing it. Also you may want to look into an aftermarket torque convertor with a higher stall speed (about 3K stall should fix the problem) Level Ten is the only source for the time being. It'll be a custom job, but should be affordable.