As to your concern about the height of your desk, I'd recommend checking out the end of this video, where I talk about how high one should be sitting relative to the table top.

Jumping in with your form intersections, there is definitely lots of room for improvement here, but I think one of the issues that is making this exercise more difficult is that you're not actually approaching them in the same manner shown in the exercise instructions. That is, you appear to be drawing your the intersection all the way through, both where visible and where not visible (due to being blocked by the form itself). While normally we certainly do stress the importance of drawing through our forms, for this exercise it's already extremely challenging on its own, so we focus only on the part of the intersection we can see.

Now I've marked out some corrections here on this page, but I felt that it was not worthwhile to try and correct everything since the issue above simply put you at a notable disadvantage. What I do want to explain however is that some students make the mistake of thinking of intersections as being between forms - so for example, a box and a sphere, or a cylinder and a cone - and they'll classify the specific kind of intersection line that results, or how they think about it, based on the pairing of forms. Rather, intersections occur across surfaces, and each form can have multiple surfaces. All surfaces are either flat (so like the faces of a box, or the end of a cone) or they're round (like the surface of a sphere, or the length of a cylinder).

A flat surface is a lot like multiplying another number by 1 - it doesn't really influence the intersection line itself, but rather allows the other surface to call the shots. So if that surface is also flat, you're going to end up with a straight line defining their intersection, but if the other surface is rounded, you'll end up with a curve. Once an intersection hits the edge of a given surface (where it's about to transition into yet another surface), that edge tells you one thing: the intersection line is going to change its trajectory sharply to follow another surface, and so you're going to end up with a sharp corner to allow for that change.

Where things get especially difficult - and I don't expect students at this stage to be comfortable with this - is when we have two rounded surfaces intersecting. This diagram demonstrates the concepts I've explained above, while also throwing in a case at the end taking a hard edge and turning it into more of a "soft" transition from one surface to another - this can help us think through how an intersection between two rounded surfaces works.

We'll be looking at this exercise in Lesson 7 as well, so we'll be able to revisit then and discuss it further.

Now, while your form intersections were admittedly rough (although this isn't especially abnormal given the difficulty of the exercise), you've absolutely knocked it out of the park with your object constructions. Throughout your work here, you've done an excellent job focusing on the core principle behind 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.

Now I really only had a couple quick points to call out. The first of these was the construction on the right side of this page - to put it simply, I'm just unclear on what you were going for with the bounding box. It looks like an orthographic plan (the box certainly isn't in perspective, as there's no convergence for the edges that move farther back in space), but then you drew the object in three dimensions inside of it. Given that the rest of your constructions don't show any issues like this, I think it's probably best we just overlook it, unless there's any specific questions or confusion you'd like to voice in relation to it.

Continuing on, looking at this tea cup, it appears that you were indeed attempting to apply the principles from these notes on constructing curves using flat edges/surfaces, but I do think that this can be improved. Here's a demo that shows how one can leverage this more fully.

As a side note to the tea cup, be sure not to leave the rim paper-thin. Anything with any thickness should have that thickness conveyed with another edge inset within the opening.

That about covers it! I'll go ahead and mark this lesson as complete.