EFI Live program (engine and trans tunes),
Edge CTS-2 InSight tuner with Cummins unlock,
VIN license for EFI Live tune,
Cummins tuning switch,
EGR & Cooler delete,
Throttle valve delete,
4" or 5" exhaust system (straight pipe or with muffler - lots of folks try the delete with the straight pipe kit and the stock muffler, then swap out the muffler later for a sound change)
EGT probe kit
Optional but it helps a lot - S&B Cold Air Intake
You will add more than what is safe for the transmission if you run it on HIGH all the time and some tuners packages are done differently. Some will build in all you want but you have to realize that's not a good deal for your powertrain.
A conservative estimate is you'll wanna be around 120HP maxed out for most tunes available on a stock transmission & lift pump. From there, you can bump it up but you do so at risk of having to rebuild the transmission and replace a lift pump and possibly injectors somewhere down the road.
When? Depends on how you drive the truck.