I managed to complete the 250 boxes challenge. It was very time consuming, so I skipped on the outlining of the outer edges of the cubes. The hatching lines didn't turn out so great. I find it hard to do so many lines parallel to each other and evenly spaced. On the last few pages I ran out of good paper an I used plain A4. I found my line tracing even more difficult to control. 

As for the cubes, after drawing a few pages I sorta came up with a system. I don't know if it was a good thing to use it, but I just couldn't unsee it. So, I start with the Y and then for the other 3 points I imagine where they would be in an isometric view. Then I tried to draw them the same amount closer to the Y intersection point. I also used ghosting and imagined where the vanishing points would be, especially when placing the inner point. Some cubes turned out horrible and others quite good. 

All in all I think it was a useful assignment and It forced me to think a lot about perspective.