You asked
What filter size does the leica elmar m 50mm f 2 8 take?
Here is what the site says about that.
From Leica Elmar-M 50mm f/2.8: Leica Elmar-M 50mm f/2.8: A prime lens by Leica for Full frame cameras, 50mm f/2.8. A collapsible 50mm, made until 2007. Specs - Maker: Leica - Focal length: 50mm (prime) - Maximum aperture: f/2.8 - Made for: Full frame sensors - Mounts: Leica M - Stabilised: no - Autofocus: no, manual focus What it frames like - On full frame (Leica M): as marked, 50mm. Cameras it fits - Leica M9: Full frame - ...
From Your first camera: How to split the budget: Spend roughly as much on lenses as on the body, or more. A modest body with a great lens takes better pictures than a flagship body with a cheap zoom. A sensible first kit: 1. The body with its kit zoom, for everything. 2. A cheap fast prime, a 50mm f/1.8 or its APS-C equivalent, for people and low light. See lenses. 3. A spare battery and a decent memory ...
Quoted from this site's pages.