I'm a huge fan of the .357, esp. if you're not a reloader.
What Cooper seems to have missed is that it's velocity that forces a JHP open reliably.
First thing, let's start with the gun. The GP100 is a damned fine revolver, esp. for the price. It's one of the smallest .357s that can handle a modest diet of the really slammin' hunting loads involving 158s doing 1,500fps, or 180s/200s at 1,300+.
I think 4" wheelguns often balance better, myself, and at that length CCW concealment in a good shoulder rig is perfectly practical. The 6" tubes will recoil even softer than the 4" and some like the balance better, it's all personal choice. You really need to rent a .357 in this heft class (Python, GP100, L-Frame) at the range, in 4" and 6"...most people seem to like the 6", I personally do well with less muzzle weight.
With something that size, similar to the Colt Python or L-Frame S&W in heft, shooting good .357 defensive fodder is quite comfortable. Some of the 110gr .357 JHPs, including the CorBon, are particularly nice. When you hear people complain about .357 recoil, most of the time they're talking about K-Frame S&Ws or similar, as with the guy with a model 66 (K-frame) below. K-Frames or mid-sized Tauruses or similar do hurt with full Magnums but the GP100 is a whole class above those.
With .357, you can also drop the power anywhere as desired below "full thunder". .38spl 148grain target wadcutters in a gun the size of the GP100 will feel like .22s going off. Mild .22s at that. There's .38 and .38+P defensive rounds that range from "decent" to "lots better than .45 hardball" that would be perfect SD loads for any beginner.
It's that enormous flexibility that's so appealing. The 357Sig is an attempt to recreate the effects of the better .357Mag 125grain loads. They didn't quite succeed, especially not if you compare .357Mag flung out of a 6" barrel.
If you do choose a smaller-frame .357 similar to an S&W K-size, that's fine, but as a beginner you'll run into recoil limits that you won't see in a larger frame until you hit the monster hunting loads. That's why people are pointing you at a GP100 or similar and as long as your personal hand size matches that gun, I would agree with that concept wholeheartedly.
There's an even bigger .357Mag frame size range out there, the S&W N-Frame or it's equivelents by Taurus. Ruger used to sell the Redhawk in .357, which is that class. By most accounts, that's overkill although the Taurus with 8 shots in that frame size at a decent price may have some appeal
. S&W does 8-shot N-frames too but they're custom shop, real pricey. The GP100 is a way better deal
.