The ivory sheers look fine, but personally I'd go with a darker color since you have so many light colors in the room - simply for the contrast. That said, while I agree with raising the curtain rod to draw the eye up, I don't agree with extending it any farther out on each side of the window. Sheers are ... well... sheer! It will be obvious that the window is no wider than it actually is so nothing is gained there. I like the plaque and mirror, and I don't think they'll seem too small once your sheers are up and fully covering the window. And I think the curtains you posted a pic of up there are perfect for the room, if you're going to stay with a light color. They're softly patterned enough that they wouldn't at all overpower the other patterns in the room, but would still add an element of interest to your window. And may I please say that your room is absolutely gorgeous. You've done a marvelous job!
P.S. Do not lower the vertical painting; it's perfect where it's hung!