Networking with various Airport Extreme/Express devices

The first generation Express was only wireless G, so that will be slower compared to everything else. If you want to only use it for Airplay, reconfigure it to Connect to your wireless network instead of bridging/extending it. Then it won't have a detrimental effect on the network. Your Extreme is at least wireless N, so that will be a decent speed connection to use as an extender.

 

I'd get a 5th Gen as the backbone definitely. The 2nd gen only has draft N versus the final spec, so that might have a difference speed-wise. Also, the 5th gen has a new antenna configuration that I've heard a lot of people comment extends their range by a large percentage. You might be able to get by with only the 5th Gen backbone and the Express connected as an Airplay device.

 

Also keep in mind that wirelessly extending your network almost cuts the bandwidth in half so if possible you would want to connect any extra Airports with an Ethernet cable. CAT5e or CAT6 at least.

With most Internet speeds you won't tell much of a difference between wired and wireless extended but when transferring between computer you will see the difference.