Hi Jay,
Welcome to the wild world of Texas Bonsai! Seriously though if you don't plan on staying through the heat of summer, you shouldn't find too many problems. Oct - May is our wet and cool season (we have two, the other being hot and dry).

Looking over your list I'd say these will do just fine:
Maples….. Trident, Japanese, and Amur
Hornbeam…. Korean
Apple…. Crab and Malus Indian Magic
Boxwood… Buxus Microphylla Koreana Nana
Blueberry….. Vaccinium Tophat (Blue Betty)
These you may have problems with:
White Cedar…. Thuja Occidentalis
Larch
Birch…. White
Spruce
The issue isn't going to be heat, humidity, or any other problem but rather your trees won't get a long enough cold dormancy period. Contrary to popular belief, it does freeze down here (tonight in fact) and we have about a 2-3 month dormancy in Central Texas. However, we'll get many many warm days inbetween, and northern trees need more cold time to keep them happy. If the travel is safe for them, most of your trees will experience the "soft seasons" of both climates and maybe they'll love it. It's interesting to think about!
I'd say another resource besides Jade Gardens located nearby in Wimberley (a great nursery!), is MBP Bonsai located in Pflugerville, only minutes away from Georgetown. Both have local experts and can help with any problems. I live in N. Austin, very near Georgetown, and I'm the president of the Austin Bonsai Society. We have a very active club and lots of members to give assistance too if needed! In addition, the Shohin Society of Texas meets in Austin and the Texas State Bonsai Exhibit is being built just outside of Austin as well.
Joey McCoy