When you figure out your bump stops, you need to care about the full compression of the shock. Not only does the bump stop stop the tire from hitting the body, it also limits the amount of up travel for the shock. You'll need 1/2-3/4" of shock showing with bump stop fully compressed statically. The extra is for the bounce you get when you hit hard.
As for your spare shafts, I'd make sure your support tool bag has the proper tools as well. For the front axle stub shafts, a 36mm socket is necessary as well as a strong breaker bar. You'll need a 12pt 12mm or 1/2" (can't remember) combo wrench to remove the 3 bolts holding the unibearing on the front. You'll need tools to remove the caliper off as well. For the rear, you'll need a 12pt 5/16 combo wrench to remove the holding bolt for the center pin. You'll need a magnet on a stick to get at the c-clips and to remove any damaged chips of steel. You'll need 1/2" socket to remove the diff cover bolts. You'll need bucket to catch the gear lube and more gear lube to add when your done. Etc.
I'd suggest that you get with someone local in your Jeep club that is doing some kind of diff work. Crawl underneath and look inside the diff housing and see how everything meshes. You may have spare shafts, but if you can't get the broken piece out of the tube, then you can't get the new in. Rear shafts break when bouncing the truck with tire speed. Try not to bounce the truck and have tire speed. This is usually a case of bump it over the ledge scenario.
Have fun, take pics and tell us all about it.
