Thank you for your service, glad to see you made the long ride home soldier!!! Welcome to The High Road. You'll find a good many of us here are vets also. Another thing you'll find is that picking a gun and caliber is an aweful lot like Ford versus Chevy (no insult intended to Dodge). We all have our favorite "flavors". What truly matters is finding the one that's right for YOU. As a CCW Instructor, I can tell you that the one that fits your hand the best, will more than likely be the one that you shoot the best. Given the fact that you'll be carrying, whether CCW or not, that should take priority. Pick what feels best to YOU, and then shoot the hell out of it.
As for single versus double action, HOW and how OFTEN you practice and train is more important than the action type. I carry a sub-compact 1911 and cock the hammer as part of my draw stroke (keeping my finger OFF the trigger until I'm coming up on target), so the double action issue ISN'T an issue for me. But, in all fairness, I've been doing it a long time.
The .45ACP is the 350 V-8 of self defense calibers. Yes, there are smaller and faster "hot-rods", but in the end, the .45 just keeps going and going, getting the job done where others have faltered. Personally, I want "old faithful" close by when the SHTF, period. You'll probably find that whatever you choose, WON'T be your last purchase, and in a month or few, this conversation may be moot