Don't waste your money on the DC header. The gains won't even be noticeable on an auto (barely noticeable on a manual as it is).
I'd get the nitrous. The 10-20hp gain from the PFC still won't be enough to get your car moving at the speed you're looking for. With the money you save from not getting the PFC and header ($700+), you can pick up a TPR or TRD
exhaust and TPR or AEM CAI
, and gain a good amount of low end (which the auto is sorely lacking) and even better top end for the nitrous to use.
Plus, your car will sound much nicer!