Here's my plan, because i'm sorta in the same situation as you are. I had a good starting point but until the other day, no direction. But now I think I've decided what i'm looking for.

I'm going to build my 350 so that it gets 1hp = 1cui or at least get it as close as possible. I'll build it so that it is a good, stout running engine. Then spray it. This way, at 350 hp, i'll be able to afford to go and cruise or what not, then when i'm at the track and i need that extra oomph that i'd have gotten from that 400-500 hp motor I can have it. Don't take my advice without some other research and what not first though. Nitrous can be the best choice you've ever made, or it can be the reason that your car is in ashes. It's all about how you deal with it and what precautions you take. A good strong 350 or 383 with a set of good flowing heads and about 50-100 shot of nitrous would get you close to where u want to be without breaking your wallet everytime you go to fill up your gas tank. JMO, and i really hope that i get some feedback on this opinion here because I can't seem to find anyone on here to comment on nitrous use as far as what's safe for a stock block, stock rods and pistons and the different types of upgraded parts.