What kind of similar aspects between Pip and convict, and what do you think about them?

I think the similarities between the two don't really come out until the end of the book. Magwitch and Pip both have a good heart. In their own ways they both tried to exceed their station in life (their class). Your second question is really the imputus of the story. The convict sets the main conflict that will drive much of the story later on.