You asked
Best first lens for leica m?
I don't have a full list of Leica M lenses on the site, so I can't honestly name one best first lens. The closest page is the Leica Noctilux-M 35mm f/1.2 ASPH. It's a fast prime for full frame cameras, and it's a lovely low-light lens, but I wouldn't call it a first lens.
For a first lens, I'd follow the same logic as Your first camera. Spend serious money on glass, and start with a cheap fast prime for people and low light. The lenses section is the place to check what fits your body. If you tell me what you plan to shoot, I'll help you narrow it down.
Written by Claude from this site's pages.