A 20-gauge shotgun and a .357 revolver are choices with which arguing would be no more than nitpicking over personal preferences.
WRT your shotgun, please give an autoloader consideration before you buy. Some folks will point at LE’s use of pump shotguns as proof of that action type’s superiority, but LE favors the pump primarily because it is cheaper. Secondarily, they use it because it is easier to feed certain specialty rounds (which you won’t be using) through a pump gun. For a self-defense gun, the very simple aim-and-keep-pulling-the-trigger-til-the-threat-is-down use of the autoloader is something very worthwhile, IMO.
Taurus makes excellent quality revolvers and has, from what I’ve heard, an superb service and warranty reputation. They also are more affordable than comparable S&W or Ruger models.
Whatever brand you go with, I’d recommend a 4"-6" barrel and a medium frame. The size and weight will help control recoil and muzzle flip and you’ll get better performance out of a decent length barrel. Short barrel “Snubbies” can be brutal to shoot with full-power 357 loads.
Older Colts like the python and trooper were fantastic, but I’m not familiar with current offerings.
I’m a big fan of Remington and Mossberg shotguns and have owned several over the years. Solid and dependable guns. I’m not familiar with their service departments, as I’ve never needed to contact them!