M3 Framelines
I'd be careful about choosing a 35mm lens. The M3 has 50, 90, and 135 framelines. The original Leica solution was external "eyes" for 35mm lenses that convert the viewfinder. There are other solutions such as external finders. If you go with an external finder, you might want to consider a 28mm lens instead, given that the 35 and 50 are fairly close.
I'd be careful about choosing a 35mm lens. The M3 has 50, 90, and 135 framelines. The original Leica solution was external "eyes" for 35mm lenses that convert the viewfinder. There are other solutions such as external finders. If you go with an external finder, you might want to consider a 28mm lens instead, given that the 35 and 50 are fairly close.