If you are building a stick home, then wire the heck out of it. If the basement is unfinished, then find a spot now for your A/V head-end and network head-end that will never be disturbed and has a lot of room for growth with high access.
Run wiring to any and all rooms that you may EVER want wiring to. Wires are cheap, repairing drywall and repainting sucks.
All this said, I'm not really comfortable with discussing your family room setup. There is absolutely nothing that I see there that is good and I would ditch pretty much every aspect of surround sound and just get a couple of bookshelf speakers and work with them, if that's even possible.
From the first photo you posted, it looks like the outer edge of the bookshelves that flank the fireplace are 18.5" wide. That would make the internal edge to edge dimensions under 17" wide. Your typical A/V receiver is 17" wide. So, an A/V receiver won't fit in your finished opening, unless I'm reading things wrong. There are two conflicting notes on this as one says to build it 19.5" wide, and one showing the frame out as 18.5" wide. Be very aware of that as it will screw you if it is wrong.
Not my decision at all, but I would have gone with a lower, wider fireplace, then dropped the TV down to a usable level and left the space wide enough to handle that. I would have put the A/V components in a completely different location than the front of the room so that they were hidden and not a part of the room.
I would have planned for the speakers as part of the fireplace/TV design from the start so that they were position properly and I would have found a place for the subwoofer, or gone with a good quality in-wall/floor unit that would have enhanced the sound of the system without impact the room layout and design.
At some point, those stupid tall fireplaces will finally go away when home designers get their heads out of their rears. Not in this design though, which is a shame.
I would recommend that you add proper 2x4 framing, centered on the opening over the fireplace, at 16" on center, for your wall mount as that is industry standard. It appears to be wider than that currently and most mounts won't span the wider distance.
I like the use of the large conduit between the equipment and the TV location. I would run it more as a straight line then the large swoop at the left side bottom, but it shouldn't any issue no matter what.
Make sure to run network to all display and equipment locations. Do NOT use wireless for any permanent devices which can be wired. Get the wire there.
Wire, wire, wire, wire, wire, wire!!! (oh, and label the wires so you know what they are and where they go!)
