I would say the important 3 in order are; Pyro, trans, and boost. Other gauges I would consider are fuel pressure, high pressure oil gauge, a real water temp gauge and possibly an engine oil temp gauge.

 

Cummins repower?

 

that'd be nice except I don't know anyone that would do a cummins swap and i don't know how to do one my self. and I don't 15 grand to drop a cummins in it sorry. haha.

 

Put the gauges in first: Pyro, trans, and boost then at a later date get the SCT with custom tunes from Eric @ Innovative Diesel. He can write you tunes that will be fine with the stock studs.
Then at a later date you can install new studs and give Eric a call for some Extreme tunes.