2500 suspension won't do much for you. That's mostly for GVWR, although the stiffer rear spring will help more with a bit of the "jello" feeling. If you just want it level, chuck a firestone ride rite air bag helper kit in there or something similar. At least when you're empty, you can drop them down to the min 10lbs and ride like a 1/2 ton again.
Best way to level a truck with a bumper tow trailer is with some kind of load equalizing hitch. It will also be much safer as the WD hitch transfers weight to the front tires which keeps your steering effective.
The most important question you need to answer first is what do you intend to tow?
Gooseneck, 5th wheel bumper pull, flat bed, enclosed trailer, and finally; the loaded weight.
Then you have to start looking at GVWR, RAWR, etc, etc.
This changes everything from brake and tire recommendations to gearing and engine choices.
Even if you do it all, you're still only LEGAL to what your truck is rated for on the door/vin.
If you get pulled over, there's a very big difference between what you can get rolling (stopping is even more important!) and what you can legally pull.
I'm not trying to sound like the weight police, but we need to know how you're going to use it before we can realistically answer your (very broad) question....