I agree you are on the right track. Have you taken a look at the Brown CDS and their common app supplemental essays? Those would also give you a head-start. Read all you can about Brown to see if there are any tips that could help you. Do you think you could be a recruited athlete? If so, that would also help with admissions. The international peer advising sounds awesome! Think about challenging yourself to continue in a leadership position where you may have an opportunity to win a national award. Congrats on all your achievements!