Okay. I'll jump in here. To rephrase your question, you are looking fo a gun for range work and home defense. Two good things to get one for. There are some things to consider.
One: There is no such thing as knockdown power. Pistol cartridges are notoriously short on power. Getting hit with one has about the same effect as getting hit with a fast baseball. Unless you hit the central nervous system, the thing that stops the perp is the loss of blood and the psychological effect of getting hit. People have been known to have their heart shot out and still have deliberate movement for 10-12 seconds. In that time they could conceivably kill everyone in you family. Other people have also been known to fall down if they just get scratched on the arm. So, shot placement is the key.
Two: Modern technology has minimized the differences between the different calibres. For example, The 230gr. Winchester Ranger T (RA45T) in .45 ACP will expand to .53 to .75 inches depending on the barrier, if any, it has to go through and will penetrate 11.6 and 16.5 inches. The 147gr. Winchester Ranger T (RA9T) in 9mm will expand to .45 tp .67 inches depending onthe barrier and penetrate 10.8 to 17 inches, again depending on the barrier. i got these numbers from the Winchester LEO ammunition catalog. There is not that much difference. So, if you are using a quality, modern hollow point design, you will be fine with either of the above two and all the usual calibres.
Three: don't worry about over penetration of the perp and worry about the rounds that totally miss the target. In most encounters very few of the bullets actually hit the target anyway. learning to shoot straight, and under some pressure, is what you need to do.
Four: The best way to learn to shoot is to get a .22lr double action/single action revolver for your first gun. Don't get anything expensive for a while yet. .22lr ammo is very inexpensive so you can shoot a lot of it and get proficient without spending a lot of cash. Find a place that has instructors and get some qualified instruction. They will cover the basics in types of firearms, safety and marksmenship. Then, find a range that will rent guns for you to try out and try some. This might cost a bit, but it could save you money in the long run. If you don't do this you might get a cool looking gun and find out later that you suck with it and should have gotten something else. Find the one that suits you the best. You'll know that by how well it sits in your hand and how well you shoot it.
Five: Cost. Ammo for different calibres cost differently. 9mm is inexpensive. You can get Winchester White Box 9mm 100 round value packs for about $11.50 at Wal-mart. .40 S&W goes for about $16 and .45ACP goes for about $18-19. If you are on a budget, and/or plan to shoot a lot, 9mm will get you more practice. Premuim defensive amo is another story. it will be expensive no matter what you choose. don't skimp on this part. Cheap ball ammo is great for the range but I don't trust my life to it. Also, don't let the cost of the gun get in the way necessarily. There are good guns for not much $. Lots of people use Star BMs and those you can get for about $150. You can also spend over $1000 for a Kimber. So, choose your budget and look around. You can find something to fit your needs.
All the above is general and well known advice.
For some personal advice, you said that you don't want to get competitive or anything. That is fine but I like the way those competitions, such as IDPA, help hone your skills. It also helps to teach you to shoot under some pressure. You are under the timer and you are judged for accuracy. This can get your nerves up a bit and simulate, to a point, what you might be feeling if you ever get in an incident. And, I have to admit, I enjoy shooting in competitions immensely. You may to.
Lastly, for home defense, nothing beats a shotgun. it has a bigger shot pattern, you don't have to be as precise, and it should not penetrate through the wall. Follow the firearm safety rules. The gun is always loaded. Never point the gun at anything you are unwilling to destroy. Don't put you finger on the trigger until you are ready to fire. The only real safety is betwen your ears. Learn safely, live safely.
If you have any other questions, feel free to ask.