Since heat rises, there is a concern about the clearances. There are two variables that you need to be concerned with: (1) the distance between the top edge of the firebox and where you put the mantle; (2) how far out from the wall the mentle will extend. If the distance in (1) is small, you need to keep the depth of the mantle small. But if the distance in (1) is large (i.e., if the mantle is to be placed fairly high), then it can be deeper. Of course, if you opt for a mantle made of a noncombustible material, you probably do not need to be concerned with these clearance issues. I do not know what reasonable estimates for these clearances are. With prefab units, the manufacturer usually provides that info in their owner manual. You might want to post your question in the chat room at hearth.com. Those are reviewed by people live and breath fireplaces, and they might give you some further guidance. The last thing you want to do is install a mantle and later find out that it gets too hot. Another alternative, if you live in a subdivision of similar homes, is to ask a neighbor if you can find one who has made renovations similar to what you have in mind. Or you could ask a chimney sweep. Sometimes, to prompte good will, they'll give you some guidance on the phone. Of if your chimney is due for a cleaning, that would be a good time to ask.

Yes we do! My actual library chairs are in my office because of naughty kitties. They will not stay out of the fireplace and they keep tracking soot all through the house. I can only imagine soot prints all over my new chairs so they have been banished to the office until I can find a cat proof solution to them getting in the fp. Toby is the Hoss Cartwright of cats so I can't imagine how he squeezes his chunky self into that tiny space.

I would leave the tv where it is. To decorate the rest of the mantle, be careful with scale. You currently have a bunch of small things so it looks cluttered. Instead of the 2 small framed pictures, replace with 2 much larger pieces, almost the same size as your tv, and move them towards the corner. They will balance out the tv on the other end. Then add a few smaller things, but not a lot. I think I counted 15 things on your mantle and not counting your tv. That's WAY too much stuff. You should have the 2 large framed pictures, the tv and 3 smaller things. Then stop.

I would paint out the fireplace "hole" black, and paint your cabinet the same color so they visually disappear - do the same with the shelves. Lean a large painting on the mantle, centering it. Add pottery on the shelves - large pieces with similar colors (one per shelf if possible) to make a statement and reduce visual clutter. Take everything else off the mantel, and then post another picture to see if more if needed.