Nice quick knit!
It doesn’t fit my baby yet, but hopefully it will this winter. When my husband noticed me knitting it, he asked “what are the chances it will actually fit when the weather’s right and not before or after?” I told him I didn’t need his input. 
I used quite a bit less yarn than the 400 yards called for.
I saw a lot of other Ravelers said the sleeves were too tight, so I cast on 36 stitches instead of 24, then increased to 38 after the ribbing (I cast on those two fewer stitches so the k2p2 ribbing would work out). In other words, I cast on the full amount of stitches for the sleeves rather than increasing up to it.
I magic looped the sleeves, which I rarely do (I’m a dpn person).
For the buttonbands, I actually counted to be sure I picked up the prescribed number of stitches. Normally I calculate a pick up rate based on my gauge and ignore the pattern, not even caring about the actual stitch count. But I figured it mattered this time because of the short row shawl collar. I ended up picking up 4 out of every 5 stitches, then fudging a bit.
I’ve used a lot of Wool of the Andes, but this is the first time I’ve used the superwash version. I think I like it -- it still feels nice and wooly. But I handwashed it for the first blocking. And I didn’t launder a swatch -- I knit a quick swatch and unraveled it before commencing with the rest of the sweater.
The buttons are not ideal, but they’re what I had in my stash. They’re 3/4” and came on a card from Joann’s, labeled “H054.”
Update the following year: we ended up not using thus sweater because I ended up not being comfortable dressing my baby in cardigans with buttons.