My 2 cents, just to hear it from someone else:
The .45 is a great personal defense round. It is that much better than a 9mm? No. Objectively, no, the FBI just spent millions of dollars to prove it. It's better to get solid center mass hits. 9mm guns generally have higher round count magazines, even if you have to carry neutered 10 round mags, I don't know how many 10 rnd .45 magazines are cost effective and or make the gun harder to conceal. The 9mm is an accurate round and has less recoil (generally speaking).
Why wouldn't I recommend a 1911 as a first gun? The low trigger weight. And for under $500 you aren't going to get a tricked out 1911, you're going to be looking at lower tier guns that may or may not be reliable out of the box. My 1911's have low single digit trigger weights, they pretty much go bang when I think about shooting. This may not be wise for a beginner. Others may disagree. It's my opinion, so blow off ya hoser.
I'd suggest any number of firearms in 9mm that will be quality firearms at around that price point. Find one that fits your hand and is comfortable to use all the features (mag release, safety if you have one, slide release). If you are unfortunate enough to live in Mass (I didn't look), your options may be limited, but 'used' guns aren't always a bad thing. I've found that 'most' guns are like motorcycles: bought on impulse, used on occasion, sold when they become a hassle to own.
Edit: to learn how to deal with flinching, long slow pulls on the trigger, when the gun goes 'bang' keep the trigger pressed. Release the trigger when you are back on target. If you feel yourself starting to anticipate, release the trigger and start again. Buy some snap caps, have someone else load them in your mags. When you hit one, you'll know it. I know I do, I, weekendracer, occasionally flinch when shooting.