I also keep my Mossberg with 00 Buck near me. You just have to be careful and not believe the myth of "just point in the general direction and pull the trigger" with a shotgun. At under 20 feet or so, a short barrel shotgun can have a spread of only a couple of inches, so you do need to aim the shotgun. As far as penetration, check out the site called "The Box O Truth". This guy built a rig with layers of drywall to do penetration testing. Here is the original link to the shotgun test. Be sure to check out the other tests, as they are interesting.
http://www.theboxotruth.com/docs/bot3.htm
A handgun can offer benefits over a long gun. You leave one hand free to use a light, phone, etc, and depending on caliber, can offer lower noise and muzzle flash. As far as models go, I love my Beretta 96 (92 model in .40 cal). The 92s are plentiful, and you can get good ones fairly cheap used. A lot of people like Glocks because they are incredibly reliable and cheap. I used to be a big caliber snob, and not shoot anything smaller than a .40 (except the .357 mag), but I have changed my views in the last few years. 9mm is fairly cheap to shoot, and not as brutal in the recoil. I bought a Taurus Milinneum Pro, but I don't care for it that much. The slide release warped on my first mag through it. Taurus is one of those brands that if you get a good one, it will last forever. If you ever get a bad one and have to deal with their customer "service", you will probably hate them.
No kidding. A friend of mine moved from TN to CA. He had his permit in TN, but still ran into nothing but problems in CA. He finally gave up.
Thanks, I will definitely check this out soon.