I’m not sure my Doespins yarn is the one I’ve linked to since the skein band says 75% merino, 25% nylon. Lovely yarn, in any case.

The written description of the Channel Island cast-on is confusing to me. I used Eunny Jang’s video (https://www.youtube.com/watch?v=up-0QOubXQ8) to see how to do it.
Also, like mags9k, I started the MC with a knit row instead of a purl to avoid having purl bumps on the outside because of the color change.

The vertical stranding technique is definitely fiddly. It certainly helps to look at the photos mentioned in the pattern. I also think that bobbins work better than butterflies to manage the CC.

I just frogged my first attempt at the vertically stranded part since I realized my tension on the CC wasn’t consistent. I need to pay attention to the tension not just on the purl stitch but also on the yarn when I take it to the back.

And…I frogged it again because I wanted to get the caston right. The right way is to hold the main yarn in your right hand as you do the Channel Island caston. Then the first main color row is a purl row and it looks right.

And…then I frogged it again because a) I forgot the 2 stockinette stitches between the 24-stitch chart and the heel so I was decreasing in the wrong place, and doing 5 reps of the 28-row chart made the socks too long for my feet. So I redid the socks, skipping rows 27 & 28 in the chart on each repetition. Now they fit perfectly and the pattern modification is not noticeable.