Well, with the new trailer out, I have new information on this part of the costume. I went through the trailer and took screen caps of Rey's costume. Here's what I found.
In this picture you can clearly see that her tunic has a side seam under the arm. The neck line of the tunic is the part that has me confused. I does look like it buttons up to some point, but the rest doesn't have any (visible) closures. My guess is that there are buttons there for her to put it on. They're likely snaps. It also looks like there may be some sort of small piping around the neckline.
My favorite part, this screen cap reveals that her tunic does NOT have any sort of cap sleeve but rather another fabric that sits under the tunic comes over the shoulder. I was having so much trouble on the mock up because of this, but this makes it so simpler!
Here's a another side view where you can see the site seam and a little bit of detail on her belt.
And a slightly better shot of her wrist cuff.
I'm still undecided on what to use for the tabbards because the viscose I got isn't crinkled. I may be forced to use cotton gauze, which I really don't want to because it won't drape the same.
UPDATE - 10/24New promo images of Rey's costume have been released. With these new photo's I've realized that the tabbards are not crinkled viscose but rater it's just gathered at the shoulder. These shots also seem to show the costume cleaner than it appears in the film which means it's a better reference for colors.