1. Tranny conv. at the same time like everyone else said, cheaper in labor
2. Running N20 on auto is okay, infact, it's safer. Any system will be fine, dry or wet, as far as you do not cross over the limit. ZEX wet kit with auto spray is good because it'll spray when you're on WOT. Some people may prefer NX, but in general, they all are okay
3. N20 can be very addictive and expensive. Yes I know, I've blown on H22 on it (not because I was crossing the line, but the fuel management was poor.
4. Piece together a good custom turbo kit and running low PSI, it'll be cost effective and more fun.