NROTC, HPSP, what?

[ryebread17]

Hello, my name is Ryan, and I am an admitted freshman for University of California - Berkeley's Fall 2012 Semester. Around September/October last year, I found out that I was accepted for the NROTC Scholarship there for Nuclear Engineering. Originally my plan was to use the NROTC Scholarship, graduate, go to the Navy Postgraduate School or some other institution to receive my masters while on active duty. However, I'm considering a different option: the HPSP Scholarship. I went to CalDay and I became very interested in BioEngineering, which I think would better help me for a career in medicine. Either way, my tuition is covered with my dad CalVet bill. It will cover tuition for public California schools, but it won't cover books, room & board, or give me a stipend. The NROTC Scholarship: I'm sure you all already know its benefits. However, there are a lot of things that I have questions about and would like clarified:

1. Should I use the NROTC Scholarship at all for my Undergrad? If I use it, I'll have to be a part of all unit activities and classes on top of trying to receive a high GPA for medical school, plus my major would be locked in one of the Tier 1s (doesn't include BioEngineering or any common Pre-Med Majors). If I use my dad's CalVet bill, I can major in whatever I feel like while pursuing Pre-Med, although there will be no stipend or book allowances.
2. How do I get the HPSP Scholarship? Are there minimum criteria? Like for the NROTC Scholarship, I needed a minimum SAT/ACT test score, GPA, and show that I'm involved/active in school. Is applying for the HPSP scholarship like that?
3. Are there limited slots for the HPSP Scholarship? How competitive is it?

Thank you in advance for those who help me decide! :)