Here's the finished item, in a size 10. This was quite a straightforward knit, even with the added complication of my having to wing the button placket modification. The body pieces are just stockinette, and the sleeves are mostly just a simple stripe pattern with the chevrons added in duplicate stitch.
I did run into one snag in that I had not enough gray yarn for this project. I used a little more than the designer intended to do the placket, of course, but I wouldn't have had enough even if I had made the sweater with a zipper as the pattern directed. And I needed just 10 grams of the extra 100 gram skein I had to buy, sigh. To make this sweater, I used 10 grams of charcoal yarn, 10 grams of cream, and 10 grams of red that all came from my stash. I had 90 grams of the new gray yarn and 30 grams of the new black yarn left, so that's a net stash increase of 90 grams for this project.
As for the rest of Bug's gift, I bought him a solarium kit from Dollarama. He'll be assembling and painting it himself, which he should enjoy, and it might be a fun way for him to learn the names and positions of the planets. Bug loves Harry Potter, and while I refuse to buy any new Harry Potter merchandise given J.K. Rowling's rampant transphobia, when I came across a perfect condition Harry Potter notebook at a thrift shop, I decided I could buy it for him in reasonable conscience, as she won't make any money from its resale.
I also picked out a gift bag with an outer space theme to go with the solarium kit, and then decided the gift was complete and Bug's tenth birthday had been duly marked.