More than a month old, but I can share my thoughts. Latest Android is quite capable, and there are a number of free apps that would help you along. Every "zone" (1 front, 2 rear for example) can be an Android tablet. There is a DLNA server/client app that would let everyone share the media on everyone else's device. You can use a small netbook also as a central spot/repository. You can use a wifi 3G router for net access. Radio is an issue unless you want to stream it via internet. Although radio for Android may not be too far off (or you can integrate into a head unit).
They pretty much all come with Bluetooth.
There are ways for Android to do real world interfacing. Or if also using a netbook, use it to control stuff via the Android tablets.
You can wait and use upcoming Windows 8 tablets as well.
Just some thoughts.