Congratulations for completing the 250 Box Challenge!

To answer your question, you should include a few boxes in your warm ups if you can. You can also do any of the exercises from lesson one in your warm ups as well. From what I can see your line work is fairly well done and your boxes are coming along well. Looking at your boxes as a whole and assuming they were uploaded in order, it looks like you made some good progress with the quality of your line work. Your lines look straighter and more confident overall as you progressed through the challenge. You also do a better job of getting your sets of parallel lines to converge more consistently towards their shared vanishing points!

One thing that I noticed about your boxes was that you were not always applying your extra line weight correctly. When you go to add weight to a line it is important that you treat the added weight the same way you would a brand new line. That means taking your time to plan and ghost through your mark so that when you go to execute it the mark blends seamlessly with your original mark. This will allow you to create more subtle and clean looking weight to your lines that reinforces the illusion of solidity in your boxes/forms. Extra line weight should never be used to correct or hide mistakes. You can also read more about this here.

Just remember that the confidence of the stroke is far and away your top priority. Once your pen touches the page, any opportunity to avoid mistakes has passed, so all you can really do is push through. Hesitation serves no purpose. Mistakes happen, but a smooth, confident mark is still useful even if it's a little off. Accuracy is something that you will improve on as you continue working through Drawabox and practice ghosting.

Now, while it is important that you use the ghosting method of each mark you make while doing Drawabox one thing you can try to help with ending your marks closer to where you want them is lifting the pen off of the page rather than stopping the motion of your arm.

Finally while your converges do improve overall I think this diagram will help you further develop that skill as you continue through Drawabox. So, when you are looking at your sets of lines you want to be focusing only on the lines that share a vanishing point. This does not include lines that share a corner or a plane, only lines that converge towards the same vanishing point. Now when you think of those lines, including those that have not been drawn, you can think about the angles from which they leave the vanishing point. Usually the middle lines have a small angle between them, and this angle will become negligible by the time they reach the box. This can serve as a useful hint.

Congrats again and good luck with lesson 2!