First of all, I don't think that furniture is comfortable enough to sit and watch TV, so the TV should be remove from that room, the purple wall paper and the purple furniture is too much, you should consider another color for that wall and the furniture against the wall it doesn't look good. What is that room at the end is kind of dark and I cannot appreciate exactly what is the purpose of that room. I'm a firm believer in skylights, we have skylights in the laundry room, kitchen, living room and office, they make a big difference. (if you cannot have skylights (or tube lights) can lights are a great option. There are a lot of great ideas from everyone. I can't wait to see the after photos.

planning to change the floor cushions to go with the curtains. can't decide on the colour combination, any suggestions will be great.

The drapes don't necessarily have to be "matchy-matchy" with the wall but they should compliment one another. If you are concerned with the drapes looking outdated overtime or if you choose to change you paint colour in the future then I would suggest getting some neutral earth tones. Depending on the style you're looking for (ex. linen, silks, sheers, modern vs. traditional, etc.)

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.