I'm kicking myself for not getting a transflective screen. I had already spent more than I wanted on my system and I felt that being up here in the Pacific Northwest I wouldn't have too much direct sunlight causing problems. I was wrong. Even fully overcast days wash out my screen (Xenarc, but similar). I think the screen is the most important part of the system because it what everyone sees and interacts with. Being in TX, with much more sunlight, I would strongly suggest a transflective screen if you can swing it.
I think iGuidance is a good choice. Works really well for me. I think I got it from buygpsnow, or something like that, bundled with the GlobalSat USB GPS receiver. It was over a year ago, though.
I started off with the TurtleBeach Roadie, but had problems with it. First of all, it's not true quadraphonic sound. The rear channels don't have any bass. I also didn't have a good way of adjusting the fade anyway. Also I noticed some pops and crackle in music every so often. So I ditched it and just used my onboard audio, running the stereo output to both front and rear. Fuller sound, and no pops and crackles. Also less bulk and frees up a USB port.
Click in my sig for a writeup on my system. Hope it helps.