I lived in Bastrop, east of Austin, for a couple years - I know Chappell Hill area - or at least, could quickly find it on a map - I think my wife and I drove thru a couple times.
I am currently keeping my ducks in two runs. A single drake (adult) with all the mature hens, and all the immature birds and the rest of the drakes in a second run. They free range together, but I have acres, so the adolescents run for the hills when I let them out, before the oldest boy can hunt them down (and thus, I free them in that order in the AM).
The very youngest of my ducks hatched 3 1/2 weeks ago, they are still in the grow out pen inside my barn overnight, but are now free ranging with the flock during the day (its how I ensure they get enough to eat each day, by ensuring there's no food competition for them at night).
Obviously, most people don't have space or resources for multiple houses, pens, and runs - but if you build a big space, you can always use some temporary fencing to partition it. I'm a fan of flexibility in runs, makes it easier to adapt to changes in flock composition.
and since you are in TX, where heat is the biggest concern, I'd look to build a big covered pen for shade and put very little (other than predator protection) into the sides - just enough to block the winds on the lower 3' or so on the sides of the prevailing winds, winter and summer. North, and East walls are the priorities - Summer winds are mostly out of the south, so not a frostbite concern, given your climate.
Hope that helps
