It's difficult to discourage you, with your choice of cameras. Unlike one poster, who appears to hate the camera (why?), most will chime in that it is a beautiful piece of design. I have the late RD ST, and I find it one of my nicest, and it is good company.
As others mentioned, it is a slippery slope. I'm fairly satisfied, with 3 bodies, that represent the Leica at 3 moments in its history (see sig). I would not add the IIIg to your list, as it isn't a user as much as a collectible, being the last of the design. The IIIa, c or f should also hold its value, as they are all desired models by both users and collectors.
If you can afford it, buy one. KEH is a good choice, as is Woodmere. I bought a couple of small items from Ritz, and they were graded properly. Stan Tamarkin also usually has a fair inventory, and there can be bargains at his auctions. I've found him to be reliable, and conservative. Don't ruch, the chase is a good part of the fun.
Harry