new to airport extreme... usb external hard drive or ethernet network???

Just bought my first airport extreme and will be networking my imac and macbook pro with it. I want to store all of my music and movies on the hard drive as well, so i want the faster transfer rates of an ethernet connection. will i be able to use one of these "network ethernet hard drives" instead of getting a traditional usb hard drive to store all my data on and still be able to have all the functionality of using the hard drive for time machine backups? also, will the wireless connection be a bottleneck making the faster speed of the ethernet network pointless? sorry about all the questions in one post, i just dont want to buy the wrong hard drive!

WD claims to have one of the fastest throughput speeds of any networking drive and they
state they are Time Machine compatible this is for their Live Book.