As chookchook said in her recommendation about painting, put a drop cloth on the floor. Get a very safe ladder. remove the lightbulbs, and cover the outlets. Turn off the electricity to the chandelier. Then spray it with a mild cleaner (I use one I found at Target that's basically water with vinegar, until it's dripping wet. Start at the bottom and work your way up, so you don't have dirty spray dripping on the bottom of the chandelier.Work your way up and down until the dripping spray is clean. The chandelier may be gorgeous and expensive, but it seems totally out of place in the architecture of the room--more at home in a chalet than a sunny room with a window wall. I would probably try to find a way to get it removed, and sell it to someone who appreciated it better than I.

Well, for lack of a better idea, since you find it a drafty little space. I'm assuming the draft comes in on the right? Most of the necessities in the area are located of the left side; i.e. vent, thermostat, light switch etc. What I would do I think is caulk up the drafty spots, maybe even add sized poster board wrapped in batting I covered in a gorgeous fuscia with diagonal grosgrain ribbons every which way covered with a heavy velvet to be attached to the area above & below the window. (Of course remove the drapes that are hanging in there). This for the purpose of using it as a pin-it board for notes. Attach a table height board covered in felt to carry across the full width of the little room. Leaving just enough space for a comfortable little antique desk chair. Paint the back wall a bright cobalt blue, paint the ceiling a silvery pearlescent white. Find a way to attach a clip-on task lamp. And stretch a heavy duty enough wire across the top of the opening and complete it with a heavy doubled velvet drape with a drooping valance. Place a swag with fringe & jewels on it to be closed when not in use. Voila intrigue is yours!

Wall sconces are for additional lighting mostly decorative you need ambient light, task light and decorative light in a space the downlights are the best way to get ambient light which the allover light you need then lamps for reading or any task that requires good close lighting and then your sconces

How about some stunning black wall sconce lights along the wall? Here's a very contemporary example... The soft grey is an excellent option, and will look stunning with green foliage against it. To give it a real 'look' I'd suggest installing some kind of black feature - whether this be painting the window frame & putting shutters either side, or the sconce lights, or a modern metal artwork. Perhaps even tall black plant pots either side of the window.