The shape of the mouth looks good from front view Max. Maybe it could be a bit wider...
What I would do (and did), is re-doing the first 4 lessons a few more times; that is the base, you are going to work with and it should be as good as possible. Save all those .blend files so you can later look at the improvements you made. But of course everybody has a different way of learning; it's completely up to you
As to your earlier question regarding the head shape, compare this (my head is far from perfect as well!):
Is there an image you are working from? I find that the face is the hardest, and I myself struggle with it. from experience with other teachers. I was always told to work on proportion first, and I think that is what you are doing. I feel the nose is too straight.
it may help to use the grease pencil. draw out the shape you want, then alter the mash.
Anyway good job, and I hope this helps you.