I know for sure you can fit 32" under the Rancho 2.5" suspension kit, that's what I have with some trimming. Depending on the kind of wheels (offset) you have, you may have to grind out a little bit of the flange on the radius arms so the tires don't rub under full turn and full compression. My offset is 3.5" (AR 63) and I had to grind a little bit. In addition, you'll also have to trim the wheel well and a little bit of body metal behind the tire, it's all trial and error.
I don't think 32" will fit with the standard James Duff 2.5" kit, which uses stock radius arms.
If you're going to run 32s, then definitely upgrade your gears to at least 4.10 and when you upgrade your gears, definitely put in at least a rear locker. If you intend on going wheeling, you'd want to have a locker installed at the time new gears are installed. It saves you the installation cost of the locker.