I know this a bit late, but I am a fourth year biochemistry major at UT Arlington.
Both UT austin UTA and UTD are wonderful schools.
First, I would advise you to join chemistry! At UTA there are over 2000 biology majors and when I took bio 1-2 micro and genetics, my classes were huge.
In chemistry, I have classes with about 20 other students which is great. I've been in a research lab with my own project since summer before my junior year and will eventually have about 2-3 publications, (it's a long project). Out of all the chemistry undergrads, about 35% are in a research lab.
I've been in 4 interviews, and the interviewers told me that is refreshing to have a different major besides chemistry and that my biochemistry background will help me a lot in med school. Also I have interviewed with one Ph.D and one MD at every school and the Ph.Ds were chemistry everytime.
Also about UTA being a commuter school, there are about 30,000 students and I'm sure we can find many activities for you to get involved.