Agree with ntsqd. Full floater and 4340 axles. Part selection depends on how serious of a build you want. Go fast is not the same as a desert racer. For a rig that never sees Baja on their typical race tracks the build would be much less expensive and still work great. Example- 300m is a better solution than 4340 (and overkill for all of us), but for an 99% of the builders just go with the imported (India) 4340. All are triple heat treated to adequate strength levels. Not sure of the RCV metal source, but they sure have a good product.? What to do - IMO just go by 4340 price.
Housing source. Why not go with one of the proven companies? I sure would not go with the one off suppliers or a vendor that specializes in EBs. Camburg, Tubeworks, Dirt Tech, Crisman, Currie, and on and on. All build to your specs, like track, tabs, Axle size (splines), R&P, third member, etc. Just read up on any of the desert builds.
Read my comment on 3 vs 4 link. Been there.