I agree with your comments Elayne. There is a lot of thinking to be done on these issues, including an aspect you raise here: "I do not belong to a political party, because all of them contain heavy elements of idealism." I think that may be a completely appropriate decision for a particular Epicurean to reach - I personally do not associate with political parties either.
But I do not think we would go so far as to say that it would be un-Epicurean to associate with a political party in every context. Often it is necessary to engage in group activity in order to offset the activities of other groups, with an obvious example being that when Greece is being invaded by Persia, the Athenians and the Spartans had better put aside their differences and form a "group" in order to fight off the attack. There's probably a boundless sliding scale of when and what type of group political activities are appropriate.
So a part of reality and living in the world is that some things can be handled individually, while some things require group coordination. As you say the "process of decision-making," presumably based on agreements as discussed in the last ten PD's, are probably going to be a distinguishing feature of normal Epicurean activities. But even saying that, there are likely to be emergencies that don't allow for extended debate and universal consent.
The bottom line is that Cicero's "one size fits all" formulation of law and justice is exactly the opposite of what an Epicurean view of the universe would support. I am attaching a clip of the Yonge translation of this passage, which indicates that this text is really from Lactantius and Augustine, which taints it even further: