You really should look up some references and analyse the skull, study it, make your observations about it, etc. And preferably real-life skulls ,as that'll give you a really good understanding of what's going on(if you look up "3D CT scans skull" or something like that, you'll find plenty of useful images I believe, aside from some regular photos of a skull).
A rough guide, perhaps.
Muscle does add height (or length rather), in a sense, especially to the chin( this is very visible from a side view). With the nose (or at least what you would mostly consider the nose) you have to keep in mind that it's all basically cartilage and fat. If you look at a skull's profile you can see that there is a small tail-like protrusion under the nasal cavity, to which the cartilage attaches; so it is basically, in most people, just below the nasal cavity.
The opening of the mouth, from my observation, tends to be on top of the upper teeth, rather than in between the teeth.
You got me with the eyes, they're pretty much in the middle of the eye socket.
The length of the skull vertically seems proportionally alright right now, I feel that the main issue now is the whole maxilla-zygomatic connection area. I'm not exactly sure how to describe that connection, but think of the maxilla like something in the shape of a horseshoe, to which the zygomatic connects to, from the middle of the side (of the horseshoe) and to the front (I guess that what I take issue to right now is that the connection seems to be at the edge of the mouth, right before the teeth, while in reality it is not like that).
Here is an edit I did to one side of the skull, to my point a bit more clear.
