Added problem with extenders is a fairly substantial throughput hit. Media servers won't be happy. Consider wired Ethernet where possible and Ethernet over power vs WiFi.
If you must go the WiFi route and don't want a throughput penalty, look into setting up the routers as a roaming network. You will have to wire all the routers together via Cat5e and not every router supports roaming (the Apple AEBS does).
http://support.apple.com/kb/HT4260