This is a really awkward space! What about trying to build a unit into the corner which seems to be dead space. This could house the television and other bits like dvr,amp etc. The unit could then extend out towards the door in length and in height either up to the start of the window or up to the start of the blinds. I would suggest drawers for toy storage and books above. In this way you leave the windows clear for light plus it looks like you have a pull down screen so the tv would be out of the way of that. This arrangement would also hide all those wires and cables! Ikea have some good examples of storage which you could adapt or copy, such as Besta which illustrates the extended toy storage. http://www.ikea.com/gb/en/catalog/products/S39927155/

You can put the TV over the fireplace, not the best situation but the way the room lays out it is the only logical place to put it. If you could you should add one additional layer on your mantel that could extend it out another 4" to deflect the radiant coming from the fireplace. I would also mount it on a slimline mounting bracket and have the bottom of the TV no further than 4" above the mantle. Ideally you want the TV to be in as straight a line as possible with your eyes. You don't want to look up too high at the TV, it's like being at a sports bar. Also if you can snake up the power and the HDMI from the cable there is a box they make that has both in one so it makes for a very clean installation.

One of the biggest cons is that above the tv is way too high for most people's optimal/comfortable viewing. There are several different opinions about the best height at which to view a tv, but generally when sitting you should be staring at the center of the screen or at the very highest at the bottom of the tv. Unless you have an unusually low-profile fireplace, watch tv standing or are like 6' 6" tall, a tv mounted above the fireplace is going to make for some uncomfortable viewing.

It depends on the style of the room as well. I don't like to see cables. I have the Cineline stand in the family room,. It swivels and I can store CDs, DVDs and the cables, behind the stand. Here is a photo of the unit in a catalog.