The best thing you could do to tie the room together is get an 8x10' rug, perhaps something with some red in it like one of these. Avoid a shag, and I'd avoid a solid-ish color. I actually think the first one would work well.

Find two bedstands, one for each side of the bed. Find two lamps for these. Although this is unconventional, we like task lamps facing the wall as they light the area well but don't blind us at night.

Get a simple clip on shade to cover the bulb on the wall.

Either get a new to you wardrobe (almira) (thrift stores) or get artistic and do something with the doors. In the past I've taken adhesive cork and covered cheap closet doors, then glued more cork on that. I used squares and made a diamond pattern on the doors. That way you have a cork board for notes, photos, etc. It's not a cheap fix, but it means you don't have to get a whole new furniture piece.

If you get a TV, place it across from the bed, that way the bed serves as a couch for watching. Just don't watch TV as you are trying to sleep (it's bad for quality sleep).

For the walls, I often suggest laminated maps. They are colorful, cover large spaces, are not that expensive, and pack easily. National Geographic sells many, many maps. Also, These maps are wild and we have one on our wall and have gifted them to our adult kids. Maps give you lots of options. Also, a map is lose enough to cover whatever it is on the wall above your desk.

Whatever you place on the wall between the two windows should be your best wall item. It would highlight your interests and tastes best if placed there.

If you add a dresser keep in mind the flow of the room. When we walk into a room we want to be able to navigate it easily. We also like designated areas, so the rug would be more under your bed and towards the windows, leaving space at the front of the room for the door to open and your desk area, wardrobe, and perhaps dresser or bookshelf. You get the idea.

I think this is a start.