Background: I've been buying and selling used cameras for close to a decade now and if there is one overriding lesson I've learned it's this, there are very few great deals. The Leica MDa was originally designed to be mounted to a microscope and thus has no rangefinder. This makes the camera pretty rare and also difficult to shoot. If you want to get one to add a rangefinder or viewfinder it's a very tricky operation and not easily done.
Your best bet is to buy a wide-angle lens and attach a viewfinder to the hot shoe. The MDa then becomes a very expensive zone focusing point and shoot camera. Like the Patek Philippe version of a Holga. I went down this path for a few years and found myself not using the setup a lot. If you're very into street photography and want to go the viewfinder route it could be doable. I shot a lot of images at arms reach and needed a rangefinder to know if I was in focus. The MDa did not excel for those shots and became less and less used.
Lastly, the allure of the camera is that it is an affordable Leica. It is affordable for a reason, it was never designed to be shot outside the lab. Let my overzealous buying purchases and lessons hopefully guide yours. I tricked myself into believing this camera was a great deal and I could overcome its limitations but I was defeated. A camera without a viewfinder or rangefinder is going to be a very difficult thing to shoot with.