As to your question about ellipse degrees in cylinders, unfortunately I'm not the one to ask - Drawabox is a course that inherently focuses on eyeballing. Ironically enough I'm saying this here, at the beginning of a critique for one of the few lessons that goes about as far as we do in this course into plotting and specific perspective, but all the same - it's not a course where you're going to learn any of the underlying mathematical rules for perspective. That said, I don't think it's something you need to worry about right now.

For your other questions:

• For actual cast shadows, it's okay to fill them in with a fineliner or a brush pen, but you should note that throughout your constructions you tend to get into a lot of form shading, which as discussed here in Lesson 2 shouldn't play a role in your drawings for this course. There are some cases where we use hatching in places like the bluetooth speaker demo, but this is generally in specific cases where we needed to give a little bit of an extra hint to the viewer that there was an abnormal, potentially unexpected curve - like a rounded corner - so the hatching helps to convey that. With curving primitive forms though (like this the body on this object), there's no need. Of course, being loose and not keeping track of what's form shading and what's a cast shadow can lead to thinking more about "how do I decorate my drawing and make it look pretty". As a side note, when you've got cast shadows falling on the ground beneath the object, you may find it comes out much better to only outline the shadow shape, and not to fill it in.

• As for next steps, unfortunately that depends wholly on what your goals are. The 50% rule plays into this a great deal, because it is largely from producing artwork myself that I've generally identified what areas I was weakest at, so I could target them with resources. So if your weakness is drawing figures, then exploring courses that get into that would be best. But if you find yourself drawing illustrations, you might find that composition is an area that is weaker. It all comes down to what you're producing on your own time.

Anyway, onto the actual critique itself - starting with your form intersections, you're demonstrating a generally well developed grasp of the relationships between these structures. I did notice some little issues, mainly where you went with a straight line when a curve (often a very subtle curve) would have been more correct, as shown here, but that's by no means abnormal at this stage. This diagram should help you better understand where to use curves, and where to use straight lines - it all really comes down to intersections occurring between surfaces rather than forms. That is to say, a cylinder has three surfaces - one flat surface at each end, and a rounded surface along its length. This results in an full intersection being a series of individual intersections that are stitched together, either with a sharp corner (when the faces in question meet at a hard edge) or a rounded corner.

I should mention however that you're currently drawing your initial linework fainter, then going back over it with a clean-up pass. As explained here in the notes, you should not be doing that. Your original linework should be confident and dark, and your line weight should be focused on clarifying how the forms overlap one another, limiting the marks themselves to the localized areas where those overlaps occur (as demonstrated here).

While I do think that you got very side tracked with the attempt at generally decorating your constructions with form shading, the constructions themselves are quite well done. You leverage your subdivision and mirroring techniques well to help make a lot of your construction's decisions before actually making your marks. That leans into the core focus of this lesson: precision.

Precision is often conflated with accuracy, but they're actually two different things (at least insofar as I use the terms here). Where accuracy speaks to how close you were to executing the mark you intended to, precision actually has nothing to do with putting the mark down on the page. It's about the steps you take beforehand to declare those intentions.

So for example, if we look at the ghosting method, when going through the planning phase of a straight line, we can place a start/end point down. This increases the precision of our drawing, by declaring what we intend to do. From there the mark may miss those points, or it may nail them, it may overshoot, or whatever else - but prior to any of that, we have declared our intent, explaining our thought process, and in so doing, ensuring that we ourselves are acting on that clearly defined intent, rather than just putting marks down and then figuring things out as we go.

In our constructions here, we build up precision primarily through the use of the subdivisions. These allow us to meaningfully study the proportions of our intended object in two dimensions with an orthographic study, then apply those same proportions to the object in three dimensions.

I'm very pleased to see you leaning into your orthographic plans, as this is an excellent way to make decisions ahead of time (especially since it's entirely separate from the construction itself). That said, this can be improved even further - though this isn't something that's explained in the lesson yet (it will be when my overhaul of the course material reaches this far, though in the meantime I explain it in my critiques.

As shown here there are a number of important landmarks that fall at arbitrary locations, and based on this orthographic plan, we don't have enough information to determine where they should be positioned when actually building the object out in three dimensions. This leads to more decisions being made closer to their corresponding marks being drawn. If however we make those decisions here, at this early stage, we already have them all pinned down before we even get to the construction stage.

Remember - precision is not accuracy. We don't have to find the specific positioning of each of these landmarks - we have to decide where they go. That means that we have the freedom to say, "39/50ths along the length of the object... that's going to be a pain to subdivide, so I'm going to put this element at 4/5ths, which is ALMOST the same thing." As long as we don't end up conflicting with some other feature that sits at 4/5ths, or something else that gets "rounded" in this manner, it's perfectly okay. As long as the decisions are made, then that's great - we have less to worry about while actually drawing.

This can be especially important when dealing with things like buttons that need to be arranged on a surface. For example, in this microphone, you ended up deciding how to arrange the three knobs along its front - that is, how much spacing fits between them, how much space there should be above the three, below the three, and how wide all three should be (there's nothing here actually guaranteeing that the three knobs are the same width).

Of course, let's say you're working on the construction and you find some decision that wasn't made yet. You've still got options. You could go back to your orthographic plan and add the decisions there before going back to your construction. That's still ideal. Another less ideal option is to just be sure to place those lines on the construction (as shown here, though of course using subdivision/mirroring to ensure that the spacing is how you want it) - while this is right on the construction, it's still separate from drawing your forms.

So! You do have a number of things to keep in mind, you are still doing well overall. I'll go ahead and mark this lesson as complete.