you can get a 33" tire no problem. the factory 275/55/20 is a 32" tire
if you look around eBay, you can get a front/rear kit that lifts anywhere from 1.5" to 3". They are essentially Leveling Kits that the 2004-2012 F-150 uses. The 3" kit should allow at least a 34" tire, and perhaps a 35" tire depending on how wide you run. The width is the killer part for fitment
I got my wife to okay letting me do a 2" lift on my Expy. I am upsizing to a 33" tire. Not looking for too much height
There is a guy here in the forums (Long EL) with a Black EL lifted 3" on 33/12.5/18" tires. looks really mean.
IIRC I believe that the factory air suspension is a inhibitor for the lift kit. It will likely need to be ditched for actual springs.
You should be able to fit a 275/60/20 tire in there without fitment issues. It's what I run on my F150 on factory 20"s.
A 285/55/20 should also fit without further modification. BFG makes their All Terrain K/O in this size.