Starting with your form intersections, overall you're doing these pretty well, although while your straight-surface intersections were fine, those between rounded forms (mainly the spheres with cylinders) were a little timid. They weren't wrong - you were going down the right path - but you just weren't willing to commit strongly enough, and instead ended up hedging a little more than you should have. Here are some corrections. The key is to think about the curvature of a given surface on the major axes of the intersection, and then find a way to blend between them with confidence.

Continuing on, your cylinders in boxes are looking very solid, with excellent convergences and proportions.

Onto the form intersection vehicles, here you definitely misunderstood what was being asked (as you mentioned yourself) - I mean, you still achieved the core of it, but you did so much more work than was actually required. For this exercise, all you really had to do was the form intersections exercise, but in the likeness of a vehicle, matching them up roughly with what you observed from a reference image. No big focus on proportions, no subdivisions required, etc.

That said, the exercise was really meant to help lay the groundwork for how the student thinks about the vehicles - first focusing on the major forms, then worrying about refining them and breaking them down into their smaller bits. For all intents and purposes, you technically misinterpreting this part had no overall negative impact - infact, your vehicle constructions as a whole are some of the best I've seen throughout all my time doing this, and it certainly lines up with the incredible amount of time you invested overall. One of the only comparable individuals would be LordNed/Matt, whose longest drawing took some 11 hours. All definitely in a similar ballpark, and it just goes to show how much time can be invested in these drawings, and how much it pays off.

It almost seems a little wrong to nitpick - things like the spokes of your bugatti's wheels lacking thickness are utterly unimportant next to just how much specifically positioned detail you packed into the drawing, whilst respecting every principle of construction. But still - even though those pieces of metal are very thin, as long as they're thicker than paper, they really ought to have a side plane to help imply their thickness and contribute a sense of solidity to that part of the structure.

The Ford Model K definitely ended up coming out a little wider, proportionally speaking. I took a look at the ellipse you used to transfer the unit onto the other axis, and as shown here it looks like the minor axis is aligned straight across horizontally, which leaves it misaligned. It should be angled a little lower to converge towards the vanishing point along the right side.

Honestly, I'm in love with your Jeep Wrangler. I think I may have a weakness for rounded corners handled well, and you've knocked them out of the park here. It gives the jeep a bulky, solid feeling and contributes wonderfully to its sense of weight. It carries through not only the main elements of the structure, but into the more minor details as well - and none of them were drawn arbitrarily or guessed at. Each one appears to first have been pinned down with straight lines, before being rounded off as a final step.

There are other small hiccups here and there - the muffler of your Honda Fireblade reading flat, the nosecone of your Panavia Tornado being a little short (and its missiles a little too big) but as a whole your work is phenomenal. All I can really say at this point is congratulations! You've completed this lesson, and with it, the whole course. It's no doubt been a demanding 5 months, but you've done an excellent job at every turn.

I look forward to whatever you end up pursuing next! Of course, the treasure chest challenge is still open to you, but it is not a required component of the course, so you can choose whether or not you wish to complete it. Either way, you've earned your completion badge. Congrats again!