I haven't fully read every post but something I haven't seen mentioned is action type and there are a few choices to consider.
Single action- The trigger only releases the hammer. This allows for a nice short and light trigger but the gun must be manually cocked before the first shot. You can either do this with your thumb or it will cock when the slide is manipulated to chamber a round. If it is left cocked, as is common practice, the safety should be left on and, of course, you must disengage the safety before the gun will fire.
Single action/double action- The trigger pull is longer and heavier for the first shot because it manually cocks the hammer just like a double action revolver. After that, however, the hammer will remain cocked for follow up shots and the trigger will be much lighter.
Double action only- The same as above except that every shot is fired double action like the first one.
Striker fired- These have a striker instead of a hammer. The gun partially "cocks" and the trigger finishes cocking the gun. The result is lighter shorter trigger but not as short and light as a single action. Many of these do not have manual safeties.
I am sure others can explain this much better but hopefully that gives you a general idea.
Since ammo cost is a concern, I tend to agree that the 9mm is a good choice. I believe it is a good compromise between cost and performance, especially with modern ammunition.
Personally, I like to follow the KISS (keep it simple stupid) philosophy when it comes to self defense. I don't like changing trigger pulls with the same gun and I don't want to forget to flip off a manual safety when woken up at 2:00 am and facing a deadly threat. My nightstand gun is a 6" Ruger GP100 357 magnum revolver. Why? Because I shoot it better than any other handgun I own, it is an effective caliber, and is extremely simple and reliable. My concealed carry gun is a full size Smith & Wesson M&P in 357 Sig which is striker fired. Again, it is a very simple firearm to operate that does not have a manual safety.
There is a long list of quality guns from reputable manufacturers, especially in 9mm. I would suggest to handle or better yet actually shoot as many as possible and figure out what action type you are comfortable with as well as whether or not you want a manual safety. Then, see which gun of that type you feel comfortable with.
"Those who would give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety."
- Benjamin Franklin