Lake Travis is not a kite-freindly spot. Last year a windsurfer was run over by a boater, he died. There are better, SAFER, places less than an hour away from Austin.
Check them out at : http://www.centexkiteboarding.com
. Winter riding in Central Texas is usually done on cold front winds. They are rideable, but, tend to be extreme. A typical cold front is 15-20, gusting to 35!
Have you considered road trips to the Coast? The winds are much steadier and the water is warmer! it is not uncommon to get steady winds 20 kts plus and air temps in high 70's.
Check out the website and you can hitch a ride down with some Centex riders, or just get some scoopage.