Honestly, I think it should be largely up to the players to work out their treaties and the terms (in a more open system, ala SE5) though I suppose it wouldn't hurt to set out some guidelines/examples.
Factions probably won't know much about each other at the start. They might have basic info on their neighbours, and out-of-character/game knowledge from the overmap, but the old Empire-wide communication networks are still in disarray at the start of the game for the first couple of turns.
I am, however, going to rework the relations.
Relations should mostly come in with regards to the Remnant. Keeping on their good side or not is entirely up to you.