Poli Sci PhD...What Are My Chances?

[Advice Appreciated]

Hi all,

First off, thanks for reading my question -- I apologize in advance if the question is too broad, please feel free to ask any follow-up questions.

I'm a senior at a top-20 US university, and I am currently doing a triple major (history, political science with an IR concentration, and environmental science).  My GPA is 3.75 (ideally I'll pull it up higher over the course of senior year).  After taking a lot of classes in various fields, doing a few internships with development-related nonprofits, and beginning to write a thesis in history (it's about Cold War proxy wars, counterinsurgency, and IR), I've decided that what I want to do is pursue a PhD in political science.  Ideally IR or security studies, because those fields interest me the most. 

In terms of extracurriculars, I've done a lot of writing-related stuff -- I'm an editor for my university's magazine, a tutor in the Writing Center, a TA for a philosophy class, and I'm also involved in a club that raises money to build schools in a developing country.  I also did research for 3 semesters on built environment/school design/architecture-related stuff just because I find it interesting.  I discovered my passion for IR pretty recently (it basically took me two years to "discover" my university's political science major), so my extracurriculars are kind of all-over-the-place in terms of area.  But I've been trying to do more political science stuff lately: I'm going to an undergrad international security conference soon, which I'm super excited for.  I can speak decent French and am currently learning Russian on my own.

What I'm curious about now is the following.  I'm already committed to completing a 2-year Master's program after graduation -- really, it's more like a service program where you teach for 2 years and take summer teaching classes to eventually receive a Master's in Education.  Essentially, I always say it's like Teach for America with a Master's degree added.  It's administered out of my current university and is fairly prestigious.  I'm excited to start it because I love to teach (one reason I want the PhD is possibly to become a professor), and I always knew I wanted to take a break for some form of post-grad service before embarking on further studies or career stuff.  But I'm wondering whether the program will impact my PhD program applications.  Will they care that it's not in a subject related to political science?  I'm sure I'll be teaching social studies or history or something of the like, but I'm a little concerned that going two years without doing research or a Master's specifically in political science will hurt my chances.  Basically, will they think I'm not "serious" enough about political science or think I'm a dilettante?  I want to convey as much as possible that I really care about this and want to research, write and teach political science.  I hope that the current work I'm doing, especially my undergrad thesis, will convey this strongly enough, but I'd appreciate any advice from people who have already completed the process.

If I manage to get good GRE scores (I haven't taken the test yet because my Master's program doesn't require it, which buys me two years), what do you think my chances are for top-15 programs in political science or security studies given my undergrad qualifications?  In the meantime, and possibly while I'm doing the Master's in Education, what can I do to advance my application and make sure I don't lose the writing/political science skills I've acquired in college?  Any advice is much appreciated, thanks again