Thanks for the replies: you guys are great!
Here's where things stand at this point. I'm probably going to get an M4 and am leaning heavily towards a 50mm lens. My style of photography, though developing, is more impressionistic, emotional, surreal, and less precise, descriptive. More Robert Frank than Walker Evans (at the risk of comparing myself to incomparable Olympians). I lean towards the 50mm because to me it seems more intimate, and human-scale, two qualities I want my photography to develop.
I am also doing this as a Leica/rangefinder experiment in which I will use this one camera, one lens pretty much exclusively for a significant period of time so as to simplify my life and get to know one style and let the equipment subside as any kind of issue. And, also very important, so that I can develop my exposure sense without a meter.
For these reasons, I am leaning towards a more vintage lens with a distinctive look and lower contrast, and am less interested in the high resolution, high contrast super sharp newer lenses. The Summicron DR is at the top of my list now; although concerned about weight and the usefulness of the close range goggles, it appears to be something I would like and that would fit well with my type of photography. Flare is definitely a concern for me and something I will have to work around and/or deal with.
If the lens or camera don't work for me, I can always sell for near what I paid, generally speaking. This, for me, is one of the real beauties of using older film equipment, especially Leica.
Any thoughts on the Summicron DR versus the Summicron Rigid? Pretty much the same optically aren't they?
Thanks again. This is fun.