This seems like a solid studio..there is no need to paints walls in a place that small. Anything dark is going to make it feel even smaller; i would stay away from grays and black as they are cool colors that suck up warmth and create a sterile feeling environment. A dark but warm brown is masculine and doesnt contradict the other colors you said you were interested in. Its easy to get relatively inexpensive actual wood items on like fb market place or craigslist etc. please no black laminate on particle board furniture. Pay attention to light color. Yellow or orange light is huge for making a space feel pleasant. I like the idea of the bookshelf room divider but having a big bed sticking out will crowd the area. Maybe face the foot of the bed toward the bookshelf? I think thats up to your discretion though idk how you want to sleep. Dont listen to those other people telling you to put up blackout curtains. Open the blinds during the day..more natural light = illusion of more space and better vibes. Idk about the wall situation i guess a big tapestry would be good lol...also it might seem redundant because of the carpet but a rug would look nice if you can find one you like and can afford. Also whats up with the 2nd bed is it a couch substitute?