Back when I was heavily into diving (15 years ago), Austin had an active dive community and great instructors at both Scubaland and Toms. I did OW, AOW, and Nitrox certs all locally.
I would recommend doing your entire OW cert through one of the local shops so when you get someplace tropical and cool, you'll be confident and can just go diving and not waste time. The local guys will spend time with you to make sure you are comfortable and safe. If you are unsure, you can schedule refreshers with them. The local shops also organize dive groups you can join on the weekends to get some extra practice with people who know what they are doing.
Diving Travis isn't everyone's cup of tea, I get it, but you're not in there that long. I'd just be more inclined to trust a local dive instructor in lake Travis over someone at a vacation resort. The skills they teach can save your life. Maybe I'm off base and they'd be pretty good anywhere, but that's me.
And CSB, my first ocean dive (Cozumel) was a few weeks after completing my OW cert locally. We got in too late for the afternoon dive, but they had a night dive scheduled with extra space on the boat. Jumping into the dark ocean that first time I was not complaining about having trained in murky Lake Travis. It gave me an appreciation for the limits of visibility and a good sense to be aware of the people around me so as not to get lost. Night diving is friggin awesome btw, and that was one of the best dive experiences I've had. Highly recommended.