Well there is first the typical rule which is to not make them too over-powered. Even though some very over-powered things like thought-bombs exist in the Star Wars universe, don't use them. Also I would like it if there was a variety of character types in the game, so if everyone was trying to play Jedi or Sith I would have to start asking them to play other things instead. In addition there are the average pbp rules that apply to all characters like not playing other people's characters etc...

In character as a Jedi or Sith you would be playing as part of a hierarchy, especially as a Sith. You're character would have to follow instructions of whatever organization or character they are loyal to, such as the Emperor or a greater lord in the case of a Sith or the Jedi Council in the case of a Jedi. Since it is more or less player-driven any other decision making will be left up to the individual characters. Feel free to collaborate with other players on whatever plots and I will try to keep information up to date as far as what everyone is doing so you can make sure what you're doing works well with what's going on (it wouldn't be encouraged to write your characters role in an invasion of Coruscant when no such invasion is actually happening).

Assallya and Tearstone, this is also my biggest concern. In order to get it running well there would have to be a handful of pretty active players with diverse characters to fill the roles that the universe needs.