Do some reading on the S&W K Frame forcing cone. If you plan to shoot light projectile weight, full magnum .357 loads like the very popular 125gr JHP you'll do best with a S&W L frame, or any of the Rugers. If you're okay with the slower but heavier full magnum loads, like the also very popular 158gr JHP & SJHP, you'll be fine with a K Frame.
Those bobbed hammer model 64s at J&G are a heck of a good deal, and, other than being .38 instead of .357, fit your stated purpose perfectly. With a good holster they're not even that hard to CCW. If I was just starting out, yet knowing what I know now, I'd get one (it'll be under $300 OTD even with shipping & FFL transfer fee), and put the other $300 & change into a good holster, a couple speed loaders, lots of practice ammo, and range time. There isn't much a Model 64 with with 158gr +P LSWCs wont do in a SD role.
PS - Don't get overwhelmed by all the the S&W K & L Frame model numbers: they just represent things like caliber, metal (SS or Blued Steel), and fixed or adjustable sights - ex: a model 19 is a 357 Mag, K frame, blued, adjustable sights; 13 same gun with fixed sights; 66 & 65 same guns, respectively, just SS. Ruger just uses a catalog number like KGP-141 for a stainless (K) 4" bbl adj. sight GP-100, or, another example KGPF-331 for stainless, fixed sight (F), 3" bbl. Why the first digit changes from a 1 to a 3 on the 3" fixed sight model, I couldn't tell you.