Jif and Scott.
Test firing different guns is a good idea. Choose what is best and most comfortable to you and family members not what others tell you to buy as you will get their favorites not yours.
In regards to the .38/.357. Many magnum calibers started off as standard ones just as many standard calibers started off as black powder rounds.. .38 special became the .357, the .44 special became the .44 magnum they simply stretched the case out. Many handguns are designed for multiple calibers. One of the more popular nowadays is the .410/.45 long colt guns that shoot a shotshell or a conventional pistol cartridge. The 9mm came from the 9mm Kurtz caliber which Kurtz means short. The .380 cartridge is simply a stretched 9mm case with more powder.
Many older revolvers and rifles were chambered in cartridges like the 44-40. This was simply a .44 caliber bullet with 40 grains of black powder same with the 45-70, 50-100 or 50-120 cartridge rifles. Generally the first number was the caliber and the second was the powder charge. You do have to be careful though as time progressed they converted some calibers and guns to smokeless ammunition which was great you got increased velocity and less fouling but modern smokeless ammunition even though it is the same caliber should not be used in older black powder guns as they will not handle it.