I am not sure where you will be fishing exactly, but redfish, speckeled trout and flounder are all fly fish game. A kayak can make it easier to reach some better areas and cover more range, but wade fishing can be very productive.
The kayak can definetly get you away from people though.

As far as rod weight, an 8 wt seems to be the most common, but a 6 ot 7 woulds also work, a big red on a 6 wt would be fun, make sure you have some backing if you got with a 6 weight. I use an 8 wt and love it. If I could figure out how to post a pic, I would show a beauty of a Spanish Mackeral I picked off in the surf.

Let me know if I can help with any other info. Oh, a good guide down in the Corpus Christi area is Dean "Slowride" Thomas, he can guide by kayak or boat.