Dave has been using Cat 5e Ethernet and plans to put it in his home, but now everyone is using Cat 6 because of gigabit Ethernet. Using Cat 6 going forward will future proof him, but at the end of the day, Wireless is a pretty strong technology. It's also way easier to setup. However, if the walls are open while he's building the house, he may as well do it. There's really no such thing as future proofing with any hardware, though. Eventually, it's going to be outdated. If Cat 6 is too pricey, 5e is fine. And he can double up on plug sockets.
What about HDMI? HDMI doesn't go far enough. He could use Baluns on either end of his cat 5e and then he can connect it to his TV. Leo says Coax is good enough, though. He should just put in a conduit so he can pull it if he wants. He should also put a cable drop in every room.