Hey! Fellow/current AmeriCorps member here. I've also accepted a position to serve with Peace Corps (currently on hold, of course). I might be biased, but I would recommend looking into Peace Corps, which sounds like a good fit given that you have the service experience (AmeriCorps) and nonprofit background. Additionally, Peace Corps would allow you to get relevant service experience while opening up so many other doors, both within nonprofit and private industry. While I have yet to depart/serve, I've heard that Peace Corps service is incredibly challenging and you get far more responsibility than you'll get at any job in the States, at least not until you're later on in your career.

Regarding Master's degree, this is something I've been thinking a lot about lately. From what I understand, a Master's in Education, in most states, is specifically to be a teacher (many salaried teacher positions require teachers to get their Master's at some point). A Master's in Leadership sounds... questionable. In my view, an MBA degree is incredibly valuable for someone that has a few years of professional experience. The MBA will open up not only doors in the nonprofit world, but the private world as well, should you ever decide to jump ship. Just make sure you go to a decent school.