If you love that wallpaper, use it in bathroom. Not really right for behind bed. I would go a drum style chandelier. In a silk pale gold. Your bed looks zen or Asian to me. I love it. But, you don't. Need to much with it. Keep it simple a more formal drape on windows, color would depend on wall color and bedding. I'm thinking a dramatic peacock satin. Use a lighter same tone on walls a rich teal. Ceiling can be gold leaf. With alight that cast shadows on ceiling at night. Then your wall paper will tie in. Furn should be mirrored.

There is contrast between the traditional furniture and the focal point of the floor which pops, draws attention. I would recover the sofas in cream colored soft fabric - suede. I would leave the curtains grey, and put down a large neutral area rug. The edges of the room would show the pattern of the floor. I would color the wall and add texture to it, but not too dark as the room will appear smaller. Add a picture and put a nice plant holder, large vase in the left corner of the room - an oriental-style vase. Or, a cream-stripe fabric on the sofas. You could go soft or bold in this room - depending on your taste.

You can work with your currant wall color or go more yellow - that is up to you. If you do decide to go more yellow. get some small inexpensive sample bottles at the paint store, paint some poster board and hang it on a wall for couple of days because getting the right buttery yellow can be hard. A soft yellow and lavender is pretty together but I also like the sea green. When you said a combo of modern and cottage - that made me think of beach cottages, which often have soft colors (including sea green) and unfussy, calm interiors. You can put a large painting up if you have the wall space for it. Many bedrooms have tall chest, dresser mirror, tall headboard and big TV, all which take up wall space. If you can hang the painting without it being crowded by any of the things I mentioned, it should look very nice. If you wish to do a curtain fabric treatment to a wall and you have the vision of what you want - then go for it. I had a friend who did that in collage - only problem was the yards and yards of fabric needed got rather expensive. So, I would start with finding bedding you love. Simple white is good, and not too expensive. However, you might find something else light that you love, or a quilt or throw for the bottom of the bed and the colors and shades might lead you in a different direction for wall color or accents. So bedding first, then curtains, then see how your wall color is and then add accents and art - although your painting can also be an inspiration for colors.

I don't think 6 sconces are too many and your placement looks fine if that's your final furniture arrangement, but I wouldn't put them in yet. I love sconces, but they can make future furniture arranging more complicated. I'd put them in after your furnishings are picked and arranged so you aren't stuck looking for pieces that work with your sconce placement. Also, it might look overdone if your chandelier and the sconces are too matchy-matchy.