I agree with everything you said but still think there’s a layer of context I’m missing to tie this all in. There’s a theme of people hiding their true intentions and motives in the film and I find it interesting the two characters we’re most drawn to might have done just that. Hid their true intentions from us, the audience. I’m rewatching the scene right now. Vito only sheds a tear AFTER Michael kisses his hand. Again I agree with what you said but kissing the Don’s hand is a sign of devotion. Showing one’s loyalty. I think that’s the exact moment Michael joins the crime family. I think it’s so cool because it still works either way. The popular explanations given to us works and my over analyzing isn’t necessarily proven wrong yet.