ill keep reading but heres my inital thoughts before looking at that picture. and lt1 fbody has a 1600 stall, a 4.3 s10 has about 1900 which is a looser converter, stock should be ok but the fbody one may help the overall feel and function of it, im told the ebay dizzys are ok, i was gonna lookinto it as my friends truck has been splitting the plstic casing in his regardless of brand, so yes stock should be fine.
roller tip stamped rockers arent gonna benefit you much besides noise, theres no lessening of resistance, only way to do that is go full roller, and im not one to talk i have stamped 1.6;s on my tbi truck right now only benefit they gave me was the different valve train angle.
if you research flowmaster is one of the poorest flowing exhausts out there, most people like it for the sound, im very vocal and hate flowmaster so i enjoy telling people its crap =) (im sorry for not being a nice person but i am a nice person overall if you knew me)
Pacesetters long tubes should sorta depend on what cam you go with, long tubes are gonna kill some of your low end power so for DD purpose it wouldnt be as beneficial id go with a mid length.
Mpfi Upgrade hell yes, iid definitely go with a tune with all this it would benefit you as would a 411 PCM swap for tuning purposes.
Volant makes the best true CAI for a vortec truck.
lastly your cam selection, breifly seeing them heres my thoughts, .480 lift is cuttin git close to max range of stock press in studs, so in light of that either pin them if you want to be cheap, or if your gonna build it proper your heads are gonna need to be magnafluxed anyhow so some screw in studs and LS2/6 springs with comp retainers would do your well with room to grow, as said you can run a stall converter with the larger cam and itll react fine, a trans cooler is recomended if you dont already have one. and imone to tune anything i modify engine internals so if it were me id be tuning both cams, i started tuning tbi for myself and very close friends DD's and such and going from a decent running truck with cam exhaust etc to a truck with the same stuff but has an extra few mpgs' , better pwoer and torque curves, idles smoother etc ive never turned back and not tuned something.
also with your exhaust, what are your plans? 2.5 " is just about damn perfect for these trucks, id go with an x or an h pipe to get everything you can out of your setup.