Yeah, what you need from the wj axle will depend on how you want to approach the build. If you want as little welding/ fab work as possible you will need: The knuckles, caliper brackets, calipers, rotors and brake lines (you can grab the unit bearing too, but you will not need it). Also, grab the lower ball joints, tie rod, and drag link. steal the steering stabilizer bracket too. It can be reused. it requires a cutoff wheel. You will need to buy from jks or another supplier, a correct length tie rod, and draglink, .25" knuckle spacers, otk track bar bracket, w and an adjustable shortened track bar. Fab work will be: welding spacers to knuckles, welding track bar bracket, weld stabilizer bracket to axle tube, and drilling rotors to 5 on 4.5. once all this is done, it should all bolt together reusing your xj shafts, and unit bearings.
If you dont mind more fab work, you can save money by cutting and sleeving the wj tie rod, and drag link, and you can build your own axle end bracket.
Best place to start is definitely with the whole front end from the wj. you wont use the center sections, gears or shafts, but just about everything else.