If the Glock fits nicely into your hands, I'd say go for it. The more comfortable with the weapon you are, the more confident you will be with it. That's as important as the reliability of the weapon IMO. The reliablity of Glocks are as good as any other top brand handgun. When there are millions of them out there, some are going to have problems.
You are already on a great thinking path. Learning how to clear jams is crutial to semi-auto SD/HD use. With a high end auto, the chances are extremely rare, but there's still a chance. I've seen FTF's that took a very long time to clear. Personally that's why I have guns everywhere
I understand that your situation wouldn't be the best for that though. I've seen problems with revolvers to. I'd say that the statistical chances that a semi auto will fail on you before a revolver are so small that it's not worth spending time worrying about. Just fire whatever weapon you get enough for you to be 100% confident in the weapon.
Reinforcing your home security is a great idea as well. Just owning a firearm isn't a cure for a security problem. The fact that you have a dog is a great thing. When you decide where and how to store the firearm look at it from three points of view:
Yours. See how easy it is to get to. Always keep it in the same place and in the same position. Practice getting to it under different circumstances. The night sights will help a lot with this in total darkness.
Your kids'. Put yourself in the shoes of a curious child. I don't know what gender, age, or maturity level your children are so I can't give a lot of advise. The only advise I can give is what my father did with my sister and I. Let the kids know about the gun. Let them see it and handle it (unloaded of coarse). Show them how to safely operate it. The most important thing is to let them know that they should never get it or touch it by themselves, but any time they want to see it all they have to do is ask. Be prepared to do that as well. That'll keep their curiosity satitsfied, but keeping it secure is important as well.
The BG's. Depending on all of the variables that make up your life you have to figure out what type of threats you are most likely to encounter. Keep the gun secure and out of sight from the BG's. Don't keep it in the same place you keep your valuables, because that's the first place they're going. If you get a safe, get one big and heavy enough that they can't carry the whole thing out, or mount is securely.
$450 is a great price for a Glock with tritium night sights in my area. I would pay that. The night sights alone are usually worth about $100. I have a set of Trijicons on my FNP-40 and I love them. I would try to ask how old the sights are. Tritium only lasts about 12 years or so. If they're still bright the'll probably be fine for many more years.
The only reason I don't like Glocks is because they don't fit in my hand. If one did the way you describe the G19 and your hand I would probably own two. There are Glock lovers and Glock haters out there. I'm neither. I've fired a few, handled and sold more than I can count, but never owned one. If you can rent one to fire, I would do that just to see how it fires, but I've never fired a gun before I bought one, and I'm happy with all of mine.
When it comes to your questions about spare magazines. All of my research has led me in the direction that it's the constant loading and unloading of the magazine that wears out the spring, not the constant pressure. Keeping spare mags loaded all the time shouldn't be a problem. I do it, as well as many others.
Good luck with whatever you decide, and keep going about things as you have been. You seem much smarter than many of the people who go looking for their first firearm. All of the above is just my humble opinion and is probably stuff you've already heard a hundred times. Just thought I would put in my $.02.