Recessed electrical and cable outlets need to be located above the fireplace, (You can hang a picture or mirror there to conceal them in the meantime.) And there needs to be a good bit of solid blocking behind the walls to accept whatever type of mounting bracket might be needed for whatever height. The fireplace should not have a raised hearth, as that puts the TV at much too high a height for comfortable viewing. There also needs to be fireplace doors that prevent the heat from escaping an roasting the electronics above. Ideally, the fireplace would be a sealed combustion chamber supplied with outside air for that combustion and then have a separate blower surround that allows you to harvest the heat to be blown into the room.