I love the wallpaper! I think you should find the rug first, and then pull a color out of it. Right now you have all 'neutral' colors, so it may depend on the colors in the surrounding rooms, if you want it all to flow.

I love this room.

The floors don't look so bad to me. Great wallpaper. A lot of colors would go with it - cream or white panels, buttery golden yellows, contrasting colors - reds, blues, greens, grays. What color are those chairs? What color of rug were you thinking of?

I wouldn't want to do a curtain color or pattern that might take attention away from the wallpaper. As mentioned above, I'd match the background of the wallpaper pattern. Take a wallpaper sample with you while you shop. The background looks white in the photos but it is often hard to tell online.

LOVE the wallpaper! You mentioned that you might like to go Neutral with the rug, which leads me to ask whether you were thinking of keeping the house neutral over all or incorporating colors??.. Perhaps you already have things in the adjoining spaces that have colors you could pull from? I like to use a dining or foyer to Introduce colors that you'll see later throughout the house. Possibly this image could provide you with a Neutral inspiration.