I ended up casting on at least 3 more times yesterday (I think actually 4) before coming up with a workable solution for the cuff of Durmstrang. First I tried it according to the pattern (after discovering that I had been switching the colors for knit and purl). The pattern worked out better, but the 100 stitches in a very nonstretchy stranded ribbing came out way too big around for my leg. I decided to cut the number of stitches down to 72 and increase on the final row. Because the ribbing was very much not stretchy, that was way too tight. At some point I think I cast on a third time, although I can't even remember why at this point. I think I had decided to just go with a plain, nonstranded ribbing. Then I finally hit upon the best solution.
I decided to go with a hemmed cuff. I cast on the 100 stitches in the pattern but on size 1's. I knit 15 rows in the main color, purled one row, and then started the stranded pattern in stockinette instead of ribbing. After finishing 15 rows in the color pattern, I folded it over at the purl row and attached the cuff to the live stitches in MC all the way around (by doing a sort of a 3-needle bind off without the binding off), with some regular 1/4-inch elastic sewn inside. **I ended up eliminating the elastic later.** I now have a snug and neat cuff! Perfect! So many reasons this worked out better, sizing being the main one but also the fact that there was a good foundation of stitches before starting the stranded pattern, rather than starting it off on round 1 which was coming out so messy.
Now, onto the actual pattern. Hopefully smooth sailing from here, although I am going to have to cast on yet again for sock 2, which is something to look forward to. At least I'll save the time of the 10 or so failed attempts and go straight for the hemmed cuff.