The 5-6" lift is preferable to a 4", since you can do a SOA in the rear, and a 2" body lift if you need more clearance. The 4" lifts keep the spring-under in the rear, so you need to buy new leaf packs, which adds a lot to the cost of the kit. The 3" body lift is a PITA vs. the 2", so going with a 4" suspension lift and 3" body lift seems like a good way to make things more expensive and difficult.
You could also just do the suspension lift and 33's will fit. I'd say 33's and 4.56's are good for a daily driver that will do just about any trails. When you get into 35's and 4.88/5.13, you are looking at dedicated trail rig use, or limited around town driving.
There are a lot of opinions about gears. None seem to be "bad", but warranty service varies by manufactuer so I'd go with one where customer service is paramount, not just based on initial price.
You could just get a standard Detroit locker or something, a locker will make it handle funny on the road, but if it's on 33's/35's, you'll have to take it easy anyway. ARB air lockers are a nice (expensive) way to get open diff road manners and locked diff capability on the trail.