My buddy and I were both in the same fleet squadron, both studied Aerospace Engineering, and had both worked at gov't funded space organizations prior to joining. Both of us had great FITREPS and, more or less identical recommendation letters. We had done the same deployments. He had a Masters, I did not. What I wish I had known in your shoes is that there are many more fixed-wing slots than rotary. In fact, there are usually only two helo slots (Sierra and Romeo) and unless they completely run out of candidates for the other platform, they're not going to consider you for a platform you've not really flown. As such, we were competing for one slot, and Masters beats no Masters. That said, they have accepted History majors in the past. YMMV!
I think your GPA will be fine, Engineering is tough. But if you're really trying to maximize your chances, knock out the Masters, get through OCS, kick ass in flight school, and go fixed-wing. Just try not to kill yourself over it (literally or figuratively), because there are more important things to life. Enjoy the ride.