So I worked out the shawl collar. As you can see, I went with garter stitch, despite all the good suggestions you all made. I just couldn't quite picture how to work out any of the pattern stitches with short rows, especially when I wasn't sure how the short rows themselves were going to turn out. Now that it's done, I think I could have make a pattern stitch work, but this is okay, too.
My husband loves this as a vest. I pointed out to him that I don't wear vests, and he said, "You would if you had one like that." Which is probably a good point. I then explained that I need a winter sweater, to which he just laughed. We share a closet, so I don't really have a leg to stand on there, either. I am forced to admit that it would make a really nice vest with just a little edging around the armholes. But I still want a sweater, so I'll be starting the sleeves shortly.
As for the collar, I'm going to try crocheting an edging all the way around. It's a little plain as is, and I've got a craving for something a tiny bit fussy.