Hello weijak! Overall you've done a pretty good job, but I'll mention all things I can catch so you can keep improving:

Starting with the form intersections exercises, one important thing on this exercise is that you should try to keep all the forms with similar foreshortening. To do this it's way easier if you stick to shallow foreshortening forms overall.

On the intersections themselves you're doing a pretty good job. So I recommend trying more challenging ones as well from now on. Like several cylinders intersecting with other rounded forms like cones or other cylinders and spheres.

One very cool thing you can do is after doing one page and finishing the intersections, is to replicate the intersections that you were having trouble with on paint 3d (which is super easy to use) or any other 3d program, so it gives you ideas of how you can approach these intersections.

On the objects themselves I think you've done a fantastic job overall! You've clearly spent plenty of time with every drawing and put a lot of effort into them! I can see what you said about the lineweight, but honestly I think they're pretty clean either way. One thing that can help to get them more clean is to approach every single line as a ghosted lines exercise. Whenever you're going to draw a new line, being it a curve a straight line or a ellipse, mark it's starting and ending points, and in case of a ellipse where does the major and minor axis ends. Then you can approach it just like a ghosted line exercise, ghost and draw it as confidently as you can. If you fail then it doesn't matter; keep going to the next line.

One thing you can do to minimize the damage the mistakes do is to break down the steps you take in even more steps. For example on this part of the drawing you could have identified 4 lines instead of 1 straight line, and then to convert each one of them in individual curves. When you do this kind of thing you can use ortographics to localize each one of these points accurately in 3d which would make your drawing more accurate as well.

Another thing I want to comment is that in some drawings you could approach them drawing through more. For example on this same drawing you could try to draw the complete structure in 3d, instead of drawing the outer lines. Like this Of course if you wanted to make it more accurate like how I mentioned earlier you could construct it with several boxes instead of one just keep in mind that when you do this kind of constructions you want to keep a balance between how accurate the drawing is and how cluttered it is. You can use as many construction lines as you want to make the drawings more accurate, but that will mean that the drawing will get more cluttered as well, and that can get out of hand very easily, so keep it in mind specially in lesson 7 as in this lesson the drawings will get much more complex.

Last thing I want to mention is that you should make sure you take the same approach with small stuff as with bigger stuff. For example in this part of your drawing you drew it accurately with your wrist. But go all the way in. If you're going to approach it as a form then draw the ellipses with your shoulders and construct it. And if you're going to treat it as texture then forget about the outline and focus on only drawing shadow shapes.

Overall like I said you're doing a pretty good job so I think you're ready for the wheel challenge. Good luck with it and keep up the good work!