If you actually haul with your truck you can't go any wider then 265mm or your back tires will rubagainst each otter when loaded. My buddy has 285s on the back of his dually but he has a 1.5 spacers. Tire with is a problem in the front as well, over 285mms on a stock offset will rub on the control arms
As for the leveling kit check out fatbobsgarage.com, they usually have a bunch of different leveling kit for 2wd trucks. Measure from the center of your axle to the lip of the fender.