The way i see it in terms of long distance chat if it is used in the final game.

OOC: for those who want to talk about the footy or whatever

Roleplayers: This way you can roleplay to your hearts content. And talk to others who are there to roleplay

Trade: this is for those selling things this is to keep out those players who otherwise will continually spam whatever item it is there selling

and OFF aswell to get rid of the annoying spam that will most likely be continually spammed across your screen.

In terms of Chat from your actual character. To those immediately around you. There should be no rules on this aside from the obvious banning of any insults or racist comments or the likes. This is because it would be impossible to police because game masters cant be everywhere. If you like roleplaying you will probably be partied up with other roleplayers anyway so the chat around you will be roleplayed.