Hi,
Photon networking, that is now part of Playmaker distribution will take care of all the chat, and player communication over the network, check the sample provided, there is a chat system implemented already!
As far as user registration and management, Scott is right, this is a sensitive topic. It depends on the platform, on the needs, on the leve of security expected.
Can you elaborate on what you expect for user management?
Bye,
Jean