The only requirement in a serious fighting weapon is reliability. I agree most folks should not carry a 1911, because of the needed knowledge base, and time to maintain it. The good news is that today we have a large number of reliable handguns to choose from. Still tops in reliability is the quality revolver, bar none. But todays selection of pistols is quite broad. One can be picky but most of them are good.
Please do not confuse civilian/police durability with military reliability and durability. Two different ballparks when applied to small arms.
Caliber is simple. For semi-auto's it's either 9 or 45. Many folks I respect like the 40S&W but I have yet to see or hear of a reason for it's existance, over the 9 or 45. Knowledgeable quality bullet selection is what is important regardless of caliber.
I have used both the 45acp and 38spl (when I did my job, the caliber did it's job) in combat, and seen the 9mm in action in several of those same actions. They were all military in nature. The handgun was only used when my primary weapon went dry at a point that the Black hats didn't want to give me time to reload soon enough for me to prevent new entries in my Health Record Book. Needless to say I succeeded, they did not. Understand I felt that when ever I was using a handgun, I was just staying alive, I fight with a rifle.
Pick a good reliable weapon for your mission statement, LEARN IT! Not just to shoot it, learn how to maintain it to it's smallest component, change your springs and in some cases, pins on schedules, and keep to it. Clean it when you use it. Just like your vehicle, teeth and body. Exactly the same issues.
As a former Marine DI this isn't advice, it's gospel. Never saw a man die BECAUSE he cleaned and maintained HIS OWN weapon. I have seen several die and get wounded because they did not.
Unless your mission requires it, large number of bullets is rarely "required", but can't hurt within reason. Don't think of possibility, stick with probability. I could get over run by an armored company of North Koreans on the way to the supermarket, but most likely will not.
I am equally at home with a 6 shot revolver, which I carried for years as I did a 8 shot 1911, 13 shot SIG 228, or a 15 shot Walther PPQ or HK. Nothing wrong with any 9mm Glock, but I subjectively don't care for them. I recommend Glocks to many folks. Owned my first Glock back in the mid to late 80s. I don't care for many compact weapons either.
Go figure.
Fred