The overall issue is "depends"....

You can do 4" lift in a Cherokee with minimum investment.

Start with a basic 3" lift and add 1" spacers under the front springs.

The 3" lift generally does an "add-a-leaf" to the rear spring pack. I went to http://www.tomken.com/ for a set of 4" leaf springs to use inplace of the add-a-leaf.

Extended rear brake lines are required.

You don't need to extend the front brake lines as long as you do not disconnect the sway-bar.

You do need to to a transmission/transfer case lowering (about 1").

Doing that, I ran 31s on my Cherokee with minor fender trimming.