*I* would put a plain valance over all the window treatments to tie them together. I don't think a roller shade under a valance would be too austere.

I'm starting to lean toward the roller shade, too. Apparently roman shades take up a lot of space at the top when open and I don't want to lose the view from the window.

I would simply install ceiling traverse rod drapery panels for the corner windows.

In my opinion, this window should be decorated in the same way as the others - with Japanese panels to the floor/stone (they will be shorter than the main ones), moving them towards the fireplace when the window is open. The difference in the length of the panels at the joint in the corner will be covered by your floor flower. The material and color of the panels are of course the same.