Wood – What kind of wood is around this fireplace

Did the transparent glass "back wall" explode because you added the front side glass doors and as a result the temperature in the fire box area went way up???

You need to consider carefully the airflow and draw requirements of the fireplace and the chimney that vents it out through the roof. Changing the design can really change the temperatures of the internal space!!

I would think that if you were to block off the far side with bricks that you may need to line the inside of the brick with special heat resistant fire bricks. Regular bricks could get extra hot and shatter too.

If you really need to have the front side glass doors make sure that there is a part of the design that permits the proper amount of air flow in around the sides of the door assembly for the chimney draw to work correctly.

1) you could use wiremold. They make 90º inside corners. I don't like it but if you have use it then it works. Better off to chop a new box in the wall exactly where you want it.

2) There are several ways to put power wiring behind the planks. EMT, ENT, wiremold...there are others less often used. You will need an extension box on the left power box to run out of.

3) The bricks around should just be a facade but why make it hard on yourself? Just bring the TV mount area out far enough to have the media box behind it.

4) Putting power in the back of the firebox will probably be a major pain. I believe that is firebrick surrounded by other brick. You may need to get a bricklayer in on this. Or at least you should study the construction of fireplaces.

I see other problems here, though. The National Electrical Code requires that no point along the floor line be more than 6' from a receptacle. If you cover the receptacles on left and right will there be other receptacles on the wall line close enough to satisfy that requirement? If not you will have to add them. Also, you can't cover junction boxes they have to be accessible inside the cabinets.