Depending how vivid your scarlet is: You can go with white or cream so it really is the accent wall and nothing is shouting for equal attention You can also go for a muted grey or beige

Well I'll try to make a 3d of the room and upload it. But that will take some time. Thank you :)

a much taller head board, something to soften up the cabinets. the bench at the end needs new fabric, and possible paint raise the bed with risers on the feet. warm neutral tones.

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.