Lost -
There's a wierd thing about Texas - people who live here tend to stay here. That does greatly influence university choice (not to mention its cheaper!) Over half my high school class went to UT plan 2. So...yes, 40% of people who get in go to college in Tx, but I bet that that percentage is fairly proportional to the # of people who apply who go to Tx universities (guessing). THe advantage doesnt come from where you go to school, it comes from your residency status.
As for GPA, unless they've change it, an A is 4.0, A- is 3.7, etc. A+ doesnt count for anything. And yes, they will figure in ALL classes taken for college credit.
Research is good. I think the only perk for doing it in Texas is that you might get to know some "key" people on the adcom before they have to consider your application (yes, contacts DO matter...)
good luck everybody,
Star