[danielf]

In addition to what others have said, I'd be hesitant to undertake any work on the chimney breast. I think that's best left to a professional. You should also consider what happens when you leave the house. The next person may well want a working fire, and your actions might render the fireplace unusable. So, either get a professional so you are sure it can still be used as a fireplace, or leave it and get a smaller tv...