Hey @tobitaurus,
Its wonderful to hear this feedback about CGCookies courses, we are extremely grateful for you sharing your appreciation, Thank you.
You would be exactly right, once you have the base head sculpted (Chapter 1), any future sculpts would start with this base.
With a base model, it is fairly easy to add/remove clay layers, inflate/deflate, grab, smooth, flatten, etc., etc., to better match any reference image before adding details to a new character.
Thanks for hanging out with us, and plough on through your Blender journey with CGCookie.
