If you want to highlight the staircase wall then your could use earthy colours such as a yellow ochre! The wall could be enhanced even more by using suitable frames and making a good collage composition for all the photos that you have (I can see many lying on the dining table). This colour would match well with wooden furnitures

OSB board will do the trick. You need another photo for us to offer a species and finish. Natural finish (clear coat...water based polyurethane finish...NO oil modified) in a low gloss or satin finish on white oak with FLOOD LIGHTS will offer the same "look" as the poor photo. Beyond that, you will need a better photo.

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.

Surbhi, The width of the room is not mentioned here but from the scale it looks like it is ~8 ft. Effective living area would be close to 90-100 sqft . Grey and darker blue may not a be a suitable palette for this area. However, the tiling is already done. You may want to go for lighter shades for the remaining areas like wall paint (try 8260 Asian paints) and maybe brighter contrasts for sofa and curtains. Bright pastel yellow or beige may be a good combination for upholstery. Thanks, Nitin CORNERSTONE DESIGNS, Bangalore