Hey, good practice man. These are the first of many more heads, I'm sure you'll see improvement as you work through the terms.
Something that helps me check the proportions of my heads, may it be front, 3/4 or otherwise, is to flip your drawing horizontally, it's a nice trick to force your eyes to see your drawings from a fresh perspective quickly, which will allow you to easily identify missproportions.
Placing the reference side to side also helps easily identify mayor points, I think I found one of the references, or at least one that looks very similar. Finding something similar, or even taking a photo yourself can help as a base.
For example, here you can see how the left part of the face doesn't keep the perspective, in the original the right eye is slightly bigger than the left one to account for the perspective among other points. The forehead is also cut short on the top but stretched to the left, and the nose and mouth could use some adjustments.
As for practice, pretty much yes to all you said.
1) Practice from references, first from real photos to understand how proportions work realistically, then also from famous artists you want to imitate to see how they stylize the specific parts. You don't have to "move" from real to stylized at some point or anything like that. When practicing you can do both, do a photo, and do one from an artist. Marc's exercices will frequently include both types through out the course.
2) Continue practicing your fundamentals, figures, volumes, 3D spatial awarness, observation, gestures, sketching, as you continue to refine all these, your overall skill will improve. Like improving the ingredients you cook with.
3) When practicing from references, you can just copy what you see to compare it, it's a good exercice, but what I found works for me better is to use the reference as a base, but still change it to force me to "get the essentials", like the gesture, mayor lines, form, structure, etc. Using a model as a base but use a different character. Marc does something similar in his studies where he will use references, but create a different character or pieces.
For example, from my Term 3: