I think that you have a very unique and compelling profile. I love your non-profit work experience and how it blends with your technical background. There are very few applicants who have actually *done* both (while there are many applicant who have tech background who only *say* that they want to do NGO work). This puts your in a very good position.
I don't think I see any real holes in your profile, although you're right about wanting to take the GMAT again. Ideally you can hit 700, but DON'T despair if you don't hit it. You can definitely get into these schools with the range of scores that you're targeting.
Re: your extracurricular activities, my advice is to keep your message pretty focused. Your current NGO work is so powerful that you don't want this message to get drowned out my too many small things. My advice is to pick one or two of these (e.g., your passion for helping youth and your theater work).
Re: schools, I think your list makes perfect sense. Maybe also target Michigan. Re: your grades and how to convert them it will depend on the school, but many like for you to simply submit your grades in % form, and they can convert or interpret as needed.
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