Nothing wrong with starting now and I promise you that you will be a tad too busy once basic training begins to worry about paleo vs non-paleo. You'll be lucky to get 15 minutes to eat your meals and you'll be so hungry you'll down everything in site and want seconds.
After basic things will easier and depending on your assignment it might be really easy.
Also with an ever-diverse military there are more options out there for dietary restrictions. I recently covered a food show for vendors to meet with military buyers and there were offerings for kosher/halal/gluten free etc. Some of those things are starting to appear in MRE's as well.
Once you get to your duty station you can just talk to the mess crew. Better yet, drop off a case of beer. Nothing wrong with having friends in the chow hall.
And if the food during basic isn't to your liking just let your drill instructors know that you won't train anymore unless you get grass fed beef with every meal.
"I did it for money and for a woman. I didn't get the money, and I didn't get the woman"