At this point, all you can and should do is focus on doing the best you can on the applications. You have solid work experience and interesting things going on outside of work, so it's a matter of figuring out how to mix both of that into your essays (and as you know there's no science to this - it's totally subjective the choices you make in terms of essay material).
As for schools, take a look at www.beyondgreypinstripes.org
which will allow you to research the schools that best fit what you want to do within non-profit (which is a very broad term and category as you know).
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