A nice down light on the coffee table would be dramatic as well. Consider using up lights in your plants. They are really small inexpensive lights that shine up into the leaves. They add a lot of drama to the room. The little desk should have some kind of small lamp on it for purposes of writing a letter or reading a book.
Art work is a tricky thing.
I don't want you to use too much because you won't be happy. When I began reading your questionnaire answers, I got a few images in my head for artwork. The really funny thing is you stated you had one of the pieces above your fireplace. The only other two places I would even consider using artwork are above the secretary and above the chest on chest. They should be related to the chair sitting by the open window.