The conditions should be proportional to the number of players but with some kind of cap.
E.g. Call for destruction of 15 home worlds seems to be very reasonable on server with 130 people.
But on server with 1300 people requirement to kill 150 home worlds would be excessive. What is a reasonable number for this case? I am not sure: maybe 25-30(?) Once people start to defend their home worlds it will not be easy to destroy them.
You made good case for Traders and small Universe.
Since the Researcher is also affected by economic conditions of the Universe some changes should apply to him as well.