Re: 5wt vs 6wt for first rod...
You have a dilemma in that you really need two rods for the two different types of fishing you plan on doing. Like another member stated, I fish a 9ft 5wt because I lived in 9ft 5wt country when I started (Idaho). I focused on trout only in medium sized rivers so one rod covered 90% of my needs.
West Texas bass and NM trout are very different. Both NM trout and their better streams tend to run small. I lived in NM for awhile and found 8ft 4wt to be the ideal northern NM rod ( I actually went down to 8ft 3wt). My Texas buddies that took me out on their lakes mostly fished 9ft 7wts for bass, a few had 6wts and even fewer had 8wts.
If it was me in your situation starting all over again would I get a 6 wt med-fast for bass and rent or borrow a 4 wt for northern NM, taking both rods with you when you go. Chances are if you get the right 6wt rod you wont need a 7 for most of your bass (and other stillwater) and can make your second rod purchase a nice 4wt for trout.