Best motorcycle to learn mechanics and riding on?

I want to learn motorcycle mechanics by buying an old body and just going through all the parts and replacing them and seeing how they work. I essentially want to rebuild the whole bike. I like the vintage models of yamaha and Honda bikes but I don't want to buy a bike that's going to be difficult to find parts for or work on for my first project. What are some bike bodies that would be easy to learn on, easy to find parts for, and easy to learn riding on? I realize it's not all going to be easy-I just figured getting some input might save me a few tears in the future.

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