Thanks to everyone for the kind words! To answer some of the questions:
It does pack down to softballish size. I haven't measured exactly but that sounds close. As far as construction, it is sewn through. I calculated 1.2" of loft for the torso and .8" for the arms and collar to put me at about 2oz. I sewed all of the horizontal baffles, filled with whatever weight for that row of compartments, sewed a vertical baffle, repeat... As far as the pattern/measurements, I had previously made a hooded parka with about 5oz of down, which turned out a little shorter than I would like and the arms were a little roomier than I wanted (the arms were easy to adjust, length I just live with). For this jacket, I figured with less down the length would be fine and I'd definitely want to take some off of the arm girth. I cut the pattern full size and took 1" off each side of the arms (and added an inch in the front and rear armpits so the holes werent' too big). Once I filled it, I sewed the first seam of the final french seam and then made a couple more seams inward until I had a fit that seemed good (taking into account I'd lose a little more with the final part of the french seam). I ended up taking about an inch off of each side in the torso and another 1/2" or so in arm girth. Length ended up perfect and the waist is fitted enough to not need a drawcord. I originally had elastic in the wrists, but ended up removing it because the wrists are small enough and come down a little bit onto the tops of my hands, creating enough of a seal that the elastic just kinda seemed annoying and unnecessary. For reference, the length at middle of the back (not including collar) on the pattern is 29" and on the finished jacket is 26".
I'm not sure the exact yardage I used, but I had an M50 quilt kit (5yds) +2 yards and made a quilt and this jacket and have some left over.
If I could make one recommendation for a jacket like this is to use a good scale. Tenths of grams is essential. I don't think any of the compartments used more than one gram of down. Overall though it's a very doable project and really due to the simplicity and lack of features is quite a bit easier than the thru hiker whitney.