I am in Zone 9, but what works for me on the cool, foggy San Francisco Bay probably wouldn't like your hot humid summers too much! However, have you checked out the Ladybird Johnson Wildflower Center? It is a wonderful Texas gardening reference. The "Explore Plants" section of their website has lots of useful information; an extensive plant database and a great "Ask Mr. Smartyplants" section. Native plants are, for the most part, excellent candidates for winter sowing, and Texas has so many showy, beautiful native plants for a gardener to choose from.