LAN / PRO DJ LINK connections

Why is a Gigabit Ethernet connection useful?
What kinds of LAN cables, LAN hubs, and wireless LAN devices can I use with the unit?
What features can I use when the unit is connected to the PRO DJ LINK network?
I can't connect my PC/Mac to the unit in the PRO DJ LINK network.
Can I link the CDJ-3000 with another type of PRO DJ LINK-compatible player such as the XDJ-1000MK2 or DJS-1000?
When the unit is connected to a DJ mixer via a LAN cable, should I connect them via an audio cable as well?