Lots of threads on this if you look around.
With a level (2" or higher) you can run up to a 35x12.5 tire on the stock wheels with 1/4" wheel spacers. You might have a slight amount of rub at full lock but thats it. If you go with aftermarket rims you'd need at least a 0 offset to avoid any rubbing at all.
I'm running 35x12.5 Toyo MT's on 20x9 -12 offset rims with a 2.5" level. No rubbing at all (with some minor adjustments). Here's a link to my thread on my wheel and tire install.
Have you decided what leveling kit to go with? I'd definitely recommend the Bilstein 5100 adjustable shocks. They are definitely the best way to level the new Rams.