Lots of good resources and advice here, shatinques, let me offer one other (well two other) points.
Get some training. It's not cheap (a good weekend class will be $400-500 plus ammo cost, which is no longer a small consideration. But considering the gravity of the choice you are making every time you choose to go armed (which, for me, is always) it is by no means too much to spend. I am a huge fan of Randy Cain, at Cumberland Tactics, but there are others who are outstanding. As always, check out the fellow's resume with great care -- lots of "trainers" out there whom I wouldn't share a table with, let alone a hot range.
In addition to training, there is some very valuable reading you can do.
I suggest Mas Ayoob, who has a web page
Mas Ayoob and has written what I consider one the essentials to armed self-defense,
In the Gravest Extreme: The Role of the Firearm in Personal Protection
There are some useful blogs, as well. (OK, forgive me if I pitch my own here:
Suburban Sheepdog )
A proper firearm and great supporting kit are important. Training and practice are more important. Mindset matters most of all. Reading and thinking about these issues in advance is crucial.