SNWMN209:
First and foremost, thanks so much for your service and I do believe your experience with the Reaper is likely to serve you well with the Phantom. For my part, I bought my P3S last Sunday after literally a year of researching and reading. I flew a blade nano indoors for the better part of a year and became very comfortable flying the simulator as well.
The only additional accessory I bought wast a 32gb Sandisk Ultra microSD card and I am very happy with that addition ($17 at Best buy). I have now logged 12 flights with my P3S and have WONDERFUL video of my new home on the coast of Maine. Very satisfying. I do expect I will add another battery or two to my arsenal, and I do imagine that filters on the cam can improve the quality of video (although I still find it AMAZING).
I do recommend being very conservative, don't test the range of the drone too early and be sure your are comfortable with the RTH function; start in beginner mode limiting your distance to 30m. You won't regret being careful. By your third or forth fly, turn off the beginner mode and set your maximum range at 120m and fly another 3 or 4 flights. From there the sky's the limit. I am delighted with the little drone, I'm sure you will be too.
Good luck, fly safe and best for the New Year.
Steve