Definitly get a brake controller. You can get by without one but you have to give yourself plenty of time to stop....and dont follow to close behind other people.
I tow a 30 ft camping trailer and when fully loaded I am running close to 10K pounds, with my 90-1/2 ton chevy w/ the 350, and dont have any trouble. It will really work the truck, but she does it.
Look into your radiator though, in the early 90's if the truck was not ordered with the towing package, it came with an extremely small radiator. I upgraded mine to a larger one, and cooling is no longer an issue. Also make sure your have/get a tranny cooler, this is a must, or you WILL fry your transmission.
One last thing, you shouldnt need an add a leaf if you center what you are towing over the trailers axles, let the trailer carry the weight, not the tongue. If you get the load in the right spot, your truck will hardly squat at all.