If you buy one of the Bessas, you should also keep in mind one major difference between the R3A and the R2 - the R3A has a battery-dependent electronic shutter, compared to the mechanical shutter of the R2 where the battery only powers the meter. This matters more to some people than others, so I highlight it only for awareness sake.

With regard to buying an eBay M3 - I started out similarly with a beat-up user M3 which I got CLA'd before using - it worked great, but I really missed the convenience of having a built-in light meter, and the film loading on the M3 is a bit more of a hassle than on the later models. If you are really intent on having a Leica body, try to pick up a cheap M6 'Classic' (pre-TTL) body instead. They are going for great prices on eBay right now, only slightly more than the cost of a good user M3 + CLA, because so many photographers are selling them to upgrade to MPs & M7s. The M6 is a great camera and preferable to the M3 for users because of the meter and faster film loading/rewind.