We carry 4000 lbs and tow 7000 lbs on a 2' extension. Going to the 19.5" wheels will give you additional capacity on your tires instead of carrying their maximum weight. Once I went to the 19.5" tires, I upgraded the shocks since there is more unsuspended weight that needs to be kept in control.
My truck came with front and rear anti-sway bars and overload spring packs due to the camper package I had selected. You may want to try your set up fully loaded and see if you need to add springs or anti-sway to yours. With just the TC, I did not need the air bags, but the additional hitch weight (even with a WDH) caused enough rear sag to put my headlights out of alignment. The bags keep the headlights where they should be and allow me to adjust for different loads.