copiah: the prices youlisted for three of the guns you identified are not all that bad, although they could be had for less. Your 686s are both good choices as they are in the medium frame (K Frame) and evolutionary developments of the Model 19s you are looking for. As for that one Model 19 you listed, the price is about right although a 3" barrel may give you more bark than bite. Since you are looking for a field piece I would recommend a 4" bbl for ease of carry and a 4" will get you that much closer to the effective velocities of the 357. I used to shoot a 4" Model 19 on the silly-wet range and could knock over the ram at 200 yds with a 200 gn boolet, so I don't think you really loose anything in a 357 by going to 4" instead of 6", except the hole the longer bbl wears in your hip.
I know how you feel about policing up your brass after a 45 shoot, and I have thought how nice it might be if CCI ever produces its aluminum cases for reloaders - then ya'll kin shootem and loosem. Same way with some of the eastern european steel cased ammo that may come in 45 acp caliber.
You also asked about S&W frame sizes: "BTW, I see S&W models referred to as the different frame size letters. What lettering does the small/med/large frame revolvers have and what is the size of the 19/686?". S&W has or had, until the 500 came out, 3 basic frame sizes: The 'J-Frame' revolvers are the smallest frames and are typically the 5 shot snubbies that come most often in 38 spl, now 357 and some of the other calibers. The 'K-Frame' is the medium frame size and is most typically seen in Model 10 38 Spl, the Model 19/686 and, I guess, now some other calibers too (but I would have to check on that); and the N-Frame is/was the largest frame revolver S&W sold and is typically seen in 357, 41 and 44 magnums. The S&W 500 is a new frame size and I don't know what it is called - they might name it the 'P-Frame', 'cause ya'll prolly need a pickup truck to haul the darn thing or maybe the 'W-Frame' 'cause you'll prolly need wheels to tow along behind ya (LOL).
HTH. Mikey.