In the rivers around here you have a couple species of bass, catfish, drum, Rio Grande Cichlid, all the different bream, several species of carp and suckers, gar, stocked trout and a few thing I'm probably forgetting. Most people target the bass but with the fly you'll catch them all eventually.
A 5wt 9' would be the right choice to start, it'll handle most of the fish you'll run in to around here on the rivers. I can bring in good sized bass, cats and drum on my 5wt.
That Cabelas combo your looking at seems to be a good sale price. I haven't used a lot of different rods to know what to really recommend. My 5wt is the TFO Pro II, medium fast and easy to cast. You don't really need a fancy reel, I rarely ever put a fish on the reel.
For river fishing (or lakes) you'll quickly see the need for a kayak or some type of boat. Most all of the river banks are private property and though there are parks, most are unconducive to fishing or wade fishing. There are a few areas on the Guadalupe River to wade, and some neighborhood ponds.
Now when I hear South Texas (Austin and San Marcos are really considered CenTex
) I think coast, and that is a whole different thing right there.