One way to handle the wifi issue is to have the wired rooms poorly serviced by wifi and focus the wifi-AP location around the rooms that aren't wired.....assuming your house is laid out with living areas at one end and bedrooms at the other (fairly common). Though if people going to be using tablets / phones with wifi all over the house.....this may not be viable.
Yeah, not really viable for that reason. My wife loves to noodle away on her iPad while we're streaming content on the telly, and we'd also both want decent connectivity to our phones.
The D-Link DIR-890L has 3 networks (2 x 5GHz and 1 x 2.4GHz), but you only sign into it once. If one of them becomes too congested it will move the users' device to another network. So if one network is streaming hi-res video, your iPad might get bumped to a 5GHz network that isn't as busy. If the user is too far away, the device has 6 antennas and can (supposely) triangulate their location and "beam" the 5GHz wifi signal toward them to extend the range. I'm yet to fully test this.
This technology is rapidly evolving.