Thanks for your post. Yes you have some strengths and weaknesses, as you describe and are aware of, but you seem to be able to further explain the reasons behind your past (grades, leaving the job etc though you may have to focus on your reason to choose the next job vs hating the prior one!), which shows a certain level of maturity, and you have a lot going for you profile-wise.
Your GMAT is excellent; higher than average at the top b-schools in the world. You have successful entrepreneurial experience with the website for finance career advancement, so that is unique and something you'd bring to a b-school classroom. The tutoring kids and the pro-bono social media campaigns are all interesting and worth highlighting in the applications. Your overall GPA is low, yes, but your GMAT does help and you can at least briefly explain the situation and why you don't feel that is fully representative of what you'll be able to accomplish in b-school.
Your school list sounds appropriate, and I think you'd have strong chances at those programs, with Booth & Stern being the most competitive on the list. (And I assume that was Fuqua at Duke you mentioned??). You could even add another top 10 program if interested, I wouldn't rule it out with what you've accomplished. Given that your long term goals sound close to the concept of social entrepreneurship, you could look into schools like Yale and Haas which are known for that (and of course there's always HBS, though challenging for all applicants.).
I would work on how you'll explain the short term post-MBA (brand management) transition into the long term goal of starting the charity. I think you can build that link of why brand management given the long term goal.... but make sure the story makes sense as it could raise some questions as it stands now. It does sound like you may have a knack for brand management though.
Good luck and keep us posted! If you'd like to chat further we have a free consult link at http://www.mbamission.com/consult.php
, or just post back here.
mbaMission Insiders Guides: http://www.mbamission.com/guides.php?category=insiders
Free Consultation: http://www.mbamission.com/consult.php