Our network is really the hub that most of our technological toys hang off of. In order to allow yourself maximum flexibility as you add more devices to your home over time you need to spend some time planning out your network in advance. Take the time to get the basic design right and you won't need to get a toupée before your time. However, you don't want to go overboard. Look at what technologies are relatively stable, what's coming down the pipeline and what's gone the way of the dodo in the last decade or two. You don't want to be the guy who ran coax networking cables throughout his entire home only to have coax die off and be replaced by twisted pair a couple of years later.
Once you are past the basic infrastructure questions and design phase you get into looking at the network as a whole. Each piece has its own role to play but they will all interact to some degree. What you need to do is think about when, how and why they will interact. Don't limit yourself to conventional thinking either. We are seeing new ideas popping up every day. Ten years ago no one would have dreamed of having their washing machine call them to tell them that the laundry is done. Game consoles didn't talk to the internet. Phones were their own distinct network. Times are changing and the possibilities are virtually endless. If you ask us soon almost every electronic device will be networked in some form or other.