Felt I should add that your Item 5 is very dangerous thinking. There's NO gun or round that you can fire that you "don't have to worry what's behind the target". Doesn't matter how weak/powerful, lead or high-tech JHP, you're responsible for everything that bullet does once it leaves the muzzle. Know your backstop, and know what's behind it, or don't pull the trigger.
Now, with that out of the way, in .357, it sounds like you want something like this: http://www.gunblast.com/Ruger-SP101-357.htm
Small frame to aid concealment, longer barrel to aid velocity w/BP, SS to resist corrosion. That would be my recommendation.