I would lean towards a diesel. I have had both with truck campers, diesel is better. 4wd vs 2wd, I have 4wd, I have never needed it. Back when I bought the truck I had a use for 4wd, but no longer. Dually vs single. Dually gives more stability. I don't have it, but don't miss it either, it makes a difference but the single still works great. 90% of my driving is with camper off.
Watch your weight. Buy the truck to fit the camper. You are looking at a LAnce, the Harley Davidson of the TC world. Good unit, but others are too, look around, you may find another with same floorplan and better weight or price.
Look at TorkLift for tie downs, and also for additional springs. They make a unit called a Super Spring, easy to install, and helpd the ride. Another good addition is to change out the bump stops. The truck will sit down a bit, but the overloads won't hit the stops. The overloads don't really come into action until that happens, so, bigger ones tame the ride even more.