A little advice
Hey, I am in your age group and I got into shooting heavily not too long ago. A couple years ago I was asking if 10mm would make a good first gun...
My very first handgun was a Beretta Minx .22 short I bought off a friend for 50$.
My first major caliber gun was a .357 Mag snubbie. Great gun, but I didn't like shooting it with .357's and it was too heavy to justify pocket carry.
With .38 specials, it wasn't bad, but I just didn't LOVE shooting it.
Well after renting and shooting dozens of guns in lots of calibers I discovered that I like .45ACP 1911's, 9mm (9X19) SIG's, XD's, Beretta's and CZ's, and .357 ruger GP100 (6 inch barrel). I have yet to have much experience with 357SIG, 10mm, .40S&W.
It's great that you are interested in various calibers (I'd love to try 9X23 as well) but I have discovered that even .45ACP gets pretty expensive to feed.
So unless you are absolutley bankrolled, I'd look at 9X19 pretty closely.
And if you are indeed, bankrolled, then may I reccomend a quality 1911 from a manufacturer like Ed Brown, Nighthawk, Les Baer, Wilson, Ted Yost, or the like?
And if you really want a "fifty" there is a .50GI 1911
http://www.guncrafterindustries.com/model1_50gi.shtml
Have fun choosing a platform and cartridge!~Nathan