Thanks for posting. First, I recommend you read this case study of a candidate who was accepted into both Harvard Business School and Stanford:http://www.stacyblackman.com/comprehens ... ies/case4/
Regarding extracurricular activities, it is always a good idea to pursue these (for business school and for outside of admissions).
To answer your last question, you have a very compelling candidacy. Don't underestimate the importance of your personal essays and recommendations though, as these are going to be critical when the final admissions decision comes around.
Conrad and the Stacy Blackman
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MBA blogger, US News and Author, The MBA Application Roadmap