If your truck were a 1500, I would suggest the WD hitch. Since it is a 2500, I would say that it's not entirely needed, but wouldn't hurt if you had one. Sway control is covered with a different piece of equipment, often-times atached to the WD hitch.
The tounge weight on your 2500 is well below what the truck is capable of, with just 4000 lbs. of trailer weight. As a matter of fact, your truck will most likely have a better quality ride with the trailer and standard hitch than with no trailer or with the trailer and a WD hitch. An open trailer has a much lower side profile than an enclosed trailer, making it much less suseptable to the forces that cause sway, also.
Now if your 2500 happens to be a standard cab, short bed(not a very common truck), you may want to consider the WD hitch and sway control, due to the extremely short wheelbase. Long beds or extra-cabs are long enough to not worry about it.
I do agree that you should be sure to set up your truck with a brake controler if your trailer has electric brakes, or make sure your trailer has surge brakes.