A 2004 Cummings is all electronic. Mine's a 1999 (same as a Dodge Ram 2000 model year) and I like it.
No DEF is good for you, bad for air.
The license you need varies on the state you live in. That is a complicated subject. Look at other threads....
I think the 5.9 with an Allison 2000 would be fine for a 28 footer.