I'm currently towing with a 2000 Ram 2500 twelve passenger, I've towed with 15 passenger vans too, there is little noticeable difference from the extra length of the 15 passenger, because the wheelbase is still the same. I like backing up with the 15 passenger more, because it seems to turn the trailer quicker, but that would probably be more personal preference.
Because the Dodge is a unibody, you'll have a hard time finding a hitch for it rated for the tow rating of the Van, I'm using a Curt that is rated for 6000lb, however it is rated for 8000lb with an equalizer hitch, which I'm using.
I've got a 360 (5.9L) in mine, and it's got more than enough power for towing, I run up and down the Shenandoahs with it reguarly, and it pulls hard and consistent, I've towed with the 318 in one, and it doesn't have enough power for an 8000lb load.
The brakes are good enough for the job, but it feels way better with good brakes on the trailer too
It likely has 3.92 or lower gearing in it already, so you'll probably be good there.
Lastly, Look up under the back where the "frame rails" attach to the body, lots of times the passengers in the back seat (Kids) spill sodas and other lovely corrosive liquids on the carpet that never get cleaned up, leading to rust through the floor boards above the rails, the rail itself is beefy and generally doesn't rust from that, but you don't want holes in the floor boards there...