I believe the advice that’s been given before (though I don’t have a link handy at the moment) for where you’re at is to try drawing some boxes for the 250 box challenge (including warmups). If your skills feel solid and your boxes are good, continue from where you left off. If you feel a little rusty and your boxes are questionable, start the challenge over but don’t redo lesson 1. If it feels like your fundamentals are sorely lacking, redo lesson 1.

From what I understand, some fraying on the far end of adding line weight is to be expected at first. The focus should be on drawing confident, straight lines— accuracy will come with mileage. For what it’s worth, I’ve also found that you can get really nice line weight variation just by changing the pressure that you write with. Doing that for me has helped my boxes look neater (because I don’t have to double up my lines) and helps me visualize the whole box before I start drawing (because I need to know what lines are the silhouette ahead of time)