I'm glad you said to keep it simple, because that's my speciality
I don't use the Nightforce ballistics, but I understand that Exbal on the PDA is nearly identical. I do use the Kestrel 3500. I don't have either my PDA or my Kestrel on hand, I'm in Michigan for a few days and they are back in Colorado. But not having them at hand will probably keep me from making it too complicated.
1) Use standard Baro pressure instead of altitude corrected. I think you just set the reference altitude to zero on the Kestrel (it's been a while I can't remember exactly). Then it will essentially tell you the Baro for zero altitude.
2) In Exbal, set your velocity, sight-in distance, Baro (not standard pressure), Rel Humidity, and temperature for your sight in conditions.
3) Then use the Rel Hum, Baro (not standard pressure), temperature etc. for your field data.
That's pretty much it.
I always use the PC version of Exbal while working up my drop charts. I'll shoot some drops and write down the scope adjustments and measure the target impact points. Then I'll adjust my BC, sight in distance and velocity until the Exbal drop chart closely matches my actual drops. Then I'll setup my PDA to match the PC version of the drop chart.
That's about it. I'll also build a spreadsheet for the drop chart that has different Baro pressures going across the top, so if my PDA takes a dump, all I need is the Baro pressure and I'm good to go. Here is an example of my emergency drop chart. It has the Baro pressure (and estimated elevation) at the top, then each MOA from -10 to +20 to match my Nightforce NP-R1 reticle.
Hope that helps,