I'd get a large cork board, dry erase board with magnets, or something like that to place above the desk so he can add whatever he likes to it. He can add posters, a large map, or flag to hang on the other walls. He also needs some sort of light near the bed. You can put in a plugin wall mounted sconce between the bed and desk, a small desk lamp on the desk, or a clip on light for the side of the desk if it's not wide enough for a lamp. The corner with the red chair is perfect for a comfy chair. If budget is an issue, you can get great deals on NextDoor or Craigslist.

Wow! Great suggestions, @calidesign. I’m kind of lost on what lamp, though. Any ideas? Pics? Thanks, again.

You can find a basic desk lamp like this at Target.