XJ and Wj are 2 different animals. Rough country may provide the appropriate length bar, but hasn't had the best reliability that I've read. If you get an adjustable, most make them so 4" is the lowest setting, but if you add lift later, you won't need a new bar, just an adjustment. You don't necessarily need quick discos with 4" but you need at least extended links. At 4", you won't necessarily need long arms off the bat, but may want them later to ease up the ride. You will probably want adjustable front lowers though, at least. Look at Teraflex for some good 4" springs on clearance. Shop for a better shock too.