Honestly, The T25-T28 rebuild is good if you are budget minded. Don't forget that if you drop extra money on a GtBB turbo, then you are taking money away from something that could possibly support that turbo's role. IE if you dont get a downpipe, how is that extra turbo going to perform.
My opinion on suspension b4 you do all the springs and shocks, is to do the front and rear sway bars, and poly bushings. I plan on installing the Abbott rear axle, at the same time as my springs and shocks too.
If I had to break it down with what you descriped it would be this.
New Stage 4 ECU after core refund:
JT downpipe without cat
Intake and Filter
Custom dual exhaust:
This sort of brings us to the end of the $2300, with maybe enough left over for springs. Seems like a healthy start, but I would definately add some items to it. What do you have ready to go, or on the car already?