I have a Macally WifiHDD connected via Cat5 to Airport Express, works fine but you need a script to trigger it for use with iTunes & AppleTv, and I need to power it via usb cord separately. To the Airport Extreme you can just connect any usb hdd. Not sure if you can connect hubs to it though, assuming you want both hdd and printer hooked up. Another solution is to complement the Extreme with and old Express as secondary router and just have the printer attached to it.