Howdy, kkilpatrick!
Barrel length is strictly a matter of personal choice. My wife likes 4 5/8" cause they are slightly lighter. I like 5 1/2" because I think they balance better (for me). However, the 7 1/2" barrels look cool!
Several things enter into caliber choice. If you're going to shoot in the SASS Classic category, you can't shoot .38/.357, because the caliber must be .40 or greater. Economics can determine your caliber choice. I don't reload, and my wife Lorelei shoots, also. We shoot .38s (in our .357s) simply because they are a LOT cheaper. I can get .38s for under 9 cents a round from a local commercial ammo loader. When you're going through 1000 rounds a month, it makes a difference! .38s typically have less recoil than .45s, so are easier to shoot, and easier to hold on target for follow-up shots. .45s make more boom and have more recoil, and are more fun for some folks. I actually like .45s more, but .38s let me shoot as much as I want to. If I win the lottery, I'll probably buy two .45 Remington pistols and a .45 Lightning rifle and shoot Classic. But I'll keep my AWA .357s and my Marlin .357!
Like Big Hext said, it's your choice. Go to a cowboy match and talk to folks about the pluses and minuses, and you'll probably find that they offer to let you try their guns. That's the best way to make up your mind!
