It looks great! I'll definitely have to swatch it, because now I really want to see it in person (especially after seeing that swatch on your cloak - wow!).
3" looks good to me. Depending on how fluffy the fur is once it's brushed out, I'd probably go with 3-4". In some photos, each side of the arm holes look like the trim is narrower than on the center front, and at the bottom edge of the armhole where the trim meets back up with itself it looks about the same width as the center front. If you're doing 3" on the center front, maybe 1.5" or 2" on each side of the arm holes so it's still 3-4" total and matches the overall appearance of the rest? But in other photos each side of the arm hole trim looks wider/fluffier, so then 3" on each side would probably be fine there too.
Edit: Just saw your latest post. (Don't know how I missed that. :facepalm ) 6" total for 3" each on the inside and outside is a good idea. I don't have any really clear photos of the inside edges, and I meant to pay closer attention to details like that last time I saw the movie, but those measurements and having it wrap around to the inside make the most sense. Let me know what you do with applying the trim to the inside of the collar seam, because in photos it looks like a continuous strip from the center front up into the collar, but I can't figure out how to have the trim wrap around the front edge and lay flat inside the collar and still look correct.
