I would paint the entire fireplace including the mantel, all trim and shelving white. I like the Whisper White, but you must bring the paint samples into the room to see for yourself. The sheen on all woodwork should be semi-gloss, easy cleaning and looks crisp. I agree with painting the walls and I would paint the part above the mantel the same color as the walls, Summer Hue is beautiful, but once again I have no idea how that would look in your room. The walls should be flat most brands make a fairly easy to clean flat. If the fireplace were the focal point of the room, it could look very cool and dramatic to paint it a very dark gray almost black. But at least in this picture it seems that the entertainment/shelving unit is the focal point. hmm .... better stop while I am ahead.

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.

I mean cost efficient way can be adopted to finish room floor and wall

Hello Sujeeta, Take care of the waves in the wall while preparing the base . The reason behind this is, when you finish the wall with the wall paper the waves in the wall is noticeable or the gap creates the bubbles in that particular area. Practically go for the pop putty or the gypsum sheet fixed for the perfect finish.