Hi yee, good job on these. You're really beginning to get the hang of the concepts of drawing. When it comes to moving on, I'd say that you should focus on your line quality. Right now the proportions are in the ball park, but the energy of the poses need some work. A thought on moving on in general; gesture, anatomy, proportion, ect... aren't really things you move on from. You get better at all of them together, while generally focusing on one at a time. At this stage you should really focus on learning how to simplify your drawings. For example, you can simplify the figure into one or two lines that show what the figure is doing. An exercise I'd recommend you do is try and simplify your figures down to a single line. This forces you to think about what the body is doing when the pose is broken down to its most fundamental elements. I've done a couple draw overs below of two different ways you could approach that pose, and one example of what I mean by simplifying the figure down to one line. Hope this helps!

I agree,the skulls are well drawn,you did pretty good at defining the plane on no 4.On the topic of male and female skull,while it helps,no I don't think it's necessary.It may help to know the more smooth brow in the female and how the male skull has more blocky feature.But I think if your goal is learning to draw portrait,it's more efficient to practice drawing portraits and knowing the plane of the face. On the topic of gesture,personally I say yes just because it interest you and you can always go back learning gesture and sharpening it (and it may be learning anatomy might improve your gesture.) On the topic of shading skill,I advise copying masters who are great at shading.I recommend John Vanderpoel,just because you are trying to learn portraits and he is excellent at designing the feature if the face to look appealing Well that's all I got,hopefully it was useful and not just a waste of time (and if it is,best regards on your art journey anyway)