From my experience you need to slow down and think about all this. You do not want to be buying a new trubo every time you add stuff. Have you taken care of the tranny?? Your tranny (auto or standard) is not going to like big injectors and a smarty. You might just want to start thinking twins, but you will need o-rings and studs then. Its a slipery slope and there is no one answer. I guess my advice is to decide where you want to be in the end (500 hp or 1000 hp), plan for that. Get all your parts together and get it done one time. I have spent way too much $$ more than once for the same part. Take turbo's, I have had three different ones, each was $1000 bucks... I could have saved 2K if I had just bought the one I wanted the first time...
I know its not fun to slow down but sometimes it has to happen.
__________________
2001 2500 4x4 QC/LWB - Mach 4's, Drag Comp, Smarty and all the stuff needed to run the mods.
13.69 @ 98 mph before the Mach 4's and Smarty