First, please fill out your profile, as you'll get better responses.
Second, large lift = vibrations = SYE + rear driveshaft = larger tires = poor performance = regearing = replacing weak Dana 35 rear axle = tires rubbing on front springs = new wheels with more backspacing = more stress on the steering = steering upgrades = $$$$
I'd recommend a lot more research before dedicating yourself to a 4" lift.
How will you be using your Jeep? What tires do you want to run to need a 4" lift?
My Ammo Can Console: http://www.jeepforum.com/forum/f12/yet-another-ammo-can-project-finished-1498520/
My 8.8 Swap: http://www.jeepforum.com/forum/f12/yet-another-ford-8-8-swap-extras-1565339/