Welcome, krazykelley. I went down this very path about six months ago; took my CCW class in February, sent in my paperwork, and bought my first gun in late March, a day after my 48th birthday.
I found these web sites extremely helpful when I was learning about handguns and ammunition, before I got my CCW and bought my gun:
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http://www.internetarmory.com/
(Read the links on "Personal Protection", "Self Defense", "Gun Selection: Self Defense", and "Ammunition: Self Defense")
http://www.corneredcat.com/
(Written by a woman who posts here, geared towards women but with a whole lot of good information for a new gun owner of either gender.)
The short answer to your questions is that there is no perfect handgun caliber or ammunition for all people at all times.
But most of the research I did and experienced people I talked with told me that most people shouldn't consider any caliber below .380 or above .45 ACP for self defense. That means you could get a .380, .38 special, .38 super, 9 mm short, 9 mm long ("Luger") .357 SIG, .357 magnum, .40 ACP, .41, 10 mm, .44 special, or .45 ACP and be within this recommended range. Lots of choices. ;-) Within that range, I've seen more recommendations for .357 magnum and .45 ACP than any of the others. .357 magnum revolvers can also shoot .38 special rounds, a real advantage if you want to start with something that's more controllable and trade up to the more powerful rounds when you've practiced for a while.
.22 (any type), .25, and .32 are widely considered not powerful enough for most self defense uses, although (almost) any gun is better than none if you're faced with a violent attacker. .44 magnum, .454 Casull, and anything higher is widely considered too powerful for most self defense uses, mostly because the rounds are too likely to go right through the bad guy and hit someone behind him. There are experienced people who will argue fiercely against that position, of course, and if you're using your gun to protect against grizzly bears, polar bears, Kodiak bears, or the like up in Alaska or northern Canada, those are good calibers to have. But the guy who taught my CCW class, a retired U.S. Marine firearms instructor, and most of the people I've talked with who have experience training people to shoot guns for self-defense recommend against carrying the higher calibers for self defense in urban or suburban areas.
For self-defense ammunition the consensus is that, for guns of the calibers above, a jacketed hollow-point (JHP) round is generally best. You could also go for semi-jacketed hollow-point (SJHP) or jacketed soft point (JSP) and not loose too much stopping power in most cases. Full metal jacket (FMJ) ammunition in these calibers is generally recommended for target practice, but not for self-defense. The practice rounds have less "oomph", and rounds packed with the same charge as a self-defense JHP have a tendency to go straight through the bad guy and hit whatever is behind him, which is *NOT* what you want to do. I won't get into brands and details; there's just too much information available from the URLs I provided and from other people here who have probably forgotten more about guns than I've ever known.
Finally, the real test of the best gun, caliber, and ammunition for you isn't what the experts say, but what you are comfortable shooting and willing to carry. Another new gun owner who recently joined this board also joined a local gun club in her area that allows members to try out any non-exotic gun at the club for free and offers assistance from experienced range masters. If you have any such opportunity in your area, I'd highly recommend taking it. If you don't, make friends with a local gun nut who has a bunch of handguns in his gun safe and is willing to take you shooting with them, and try them all out.
Best wishes figuring it all out.
And even if I were, the nearest rental range is hours away, so my only option really is finding out what other people think (usualy by silently lurking on forums like this 
).