Not a touring expert here but I've done a few week-long trips over the years. I would pick a handful of places I'd really like to visit along the way and then try to build the route out from there. If a particular place is too far out of the way, it could be left as optional. Your ride would seem to have no shortage of things to see. I personally would want to pass through the Guadalupe Mtns of W Texas, Carlsbad caverns in S. New Mexico and perhaps up to Santa Fe/Taos, etc., then of course the Grand Canyon in Ariz. and maybe canyon country of southern Utah ... OK, I've probably just made it worse.