OK so I want to go wide. I have an M2, M3, and OM2's. So far I've never gone wider than 35mm. I'm not sure if I want 21mm or 28mm but I want to try both. I don't need speed nor does it have to be tiny. Faster and smaller lenses are great but that is not my priority. Just the focal length and decent performance at moderate apertures (f4 - f5.6...don't think I can afford much faster, really).

I have two practical options:
1. RF route: CV with external viewfinders.
Leica is pretty expensive. ZM is better priced but CV is by far cheaper. If I go rangefinder, then I'd start with CV then eventually "upgrade" to ZM's or Leica's if I feel that there is a benefit for whatever reason (optics, build, bling factor). I haven't researched the build/optical qualities of CV vs ZM vs Leica at these focal lengths.

2. Go Zuikos.
Fast Zuikos are expensive (but much cheaper than Leica/Zeiss) so I can go with the slow ones for not that much money then "upgrade" to fast ones or perhaps rangefinder ones too. I haven't researched how these compare to RF designs, but I hear good things about zuiko wides.

SLR vs RF is a personal choice and it depends on application.

1. I want to be able to shoot at close-ish distances. Are the external viewfinders pretty bad for this? ~how much error would I expect? I imagine that this is hard to quantify. I'm thinking 1-2 meters. This screams SLR to me.

2. I hear RF wides are better. They have a design advantage but many RF lenses are retrofocus too. How are the Zuikos at f4 and f5.6. In terms of sharpness/contrast/distortion. They're bigger no doubt, but still managable. I'd probably go with the f3.5/f2.8 lenses since they are cheaper.