Yes, the academy will ask for all your extracurriculars from your high-school years.

Will your residency legally change when you go to school?  I would doubt it, but be sure.  You would apply to whichever representatives work for your state (and district) of residency. (probably Texas, but double check)

Boarding school shouldn't lower your chances as long as you keep your grades up, take the challenging classes, and stay involved in extracurriculars there.