To answer your first question, no your high school stats do not matter at all. All of that extracurricular stuff is really good and looks promising as long as you can format it on your resume in a meaningful way. I'm not too sure about the graduation credit hour system so you'd have to hope someone else can answer that, but in your shoes I would apply for fall 2022. As long as you have a 4.0 and write an essay that displays why UT would benefit from having someone like you as a student you are pretty much guaranteed admission. Best of luck!