Nice, solid construction here! However, I don't know if one really needs these circles at the first step. They reflect some of the geometry behind these facial features, but it's not defining. (except the eye, of course). I am, myself, not a pro, but from the books I saw, they seem to start with large volume blocks or boxes, not flat circles. (except for the eye, again) In case of this tutorial that would be step 2. Anyway, that was useful, thanks!
Yes, the circles thing is not meant to be a precise construction method, it's more like a cheat sheet to help visualizing the basic volumes when shading. Again, i didn't invent this method, i found it somewhere (somebody suggested Loomis books in a comment, i think they might be right) and it has been a helpful trick for me.