Definitely figure out the axle thing first. Then get it under your rig, then figure out your springs, then figure out your steering. It's a good idea to have a general idea of what you want before you start, but there is no tried and true on a SAS. Everyone did something different and unlike toyotas and chevys there is no kit, so it's one of this keep throwing thing at it until it fits.
As far as the axles, google. I found several different site with info on how to identify this axle or that one.