I love my XJ, i am basically stock, but from the pic, you can see everything i have done so far... i have no lift and my XJ will still go places that i will not yet...
My XJ is a 2000 with about 216K miles on it and still runs strong with regular maintenance
as it was said before, think about it systematically and the research will pay off... for example, you can go from stock to about 3 inches with no changes to the drive-line, after that you need to re-angle the rear axle, get a SYE, longer drive-shaft, ect...
when you get your XJ work backwards on your build... decide what you want it for then decide how you want it to look and perform then what size tires so you can find the minimum lift, ect...