Okay, I think I've got a decent collar on this thing, mostly by improvisation.
I picked up 3 stitches for every 4 rows along the front. Spacing them out by the mantra "(1)slipped stich - (2)in between - (3)slipped stitch". In the end I got 56 picked up stitches along each of the fronts, 24 stitches along the back neck. Picked them all up first, then broke off and started knitting the collar along the back neck.
Used size 9 needles to knit the ribbing. Made it look neater (I must knit ribbing really loose or something.)
I started off picking up 4 stitches at the end of each row. But when I got halfway down the fronts, I upped that to 6 stitches at the end of each row. Once I got to the bottom, I turned around and started binding off immediately. I cast off 6 stitches at the beginning of each row.
I still kept ending up with that hole at the transition between the previous bind-off and the new bind-off. So I just fiddled with it until it looked nice. It was the loop from the previous bind-off that would always stretch out and get all huge and make the hole. So what I did was reach down underneath it to grab another loop of the yarn that was making that stitch, and wrap it around my right needle again, cinching that stitch tight. Then slipped the next stitch onto the right needle, and pull the double-loops over that. No more hole.
I kept up with binding off 6 stitches at a time, until about halfway up when it was starting to look like the collar would get too huge, so then started binding off 8 stitches at a time, then 10, then finally I was done. And it looks fine.
So now I need to sew the side seams for the sleeves. I'm leaving the bottom open for a little while, in case I want to add even more to the length. Of course my new problem is that I think I'm going to run out of yarn. So the bottom ruffle will likely be in another dye lot. But that'll be the best spot to get away with that - I hope!