I'd suggest dark red curtains if you need curtains at all -- the windows are beautiful as they are, and I'm not sure whether some kind of blind might not give you the ability to darken the room when you want to. On the wall, if you are real fans of any movies or TV shows, three big posters would be fun. Otherwise, I would still suggest using three pieces of art there of that size, all equal in size and somehow relating to each other. Three floral works, or three works in the same style, perhaps. I think a large plain textured rug in a light neutral from one of the cushion fabrics would tie the space together well. You might also consider a lovely low coffee table on the rug to lay out your snacks and drinks for serious media nights.

Consider Grey or white. U could also use geometric or any pattern in mint green

Choose a contrasting color to the sofa, while choosing keep light requirement of room in view. So for that you should use light color curtains only, such as light golden, cream, Off-White.

It would be great if you can share the picture. Things are clear in a better way when you see them visually.