At the end of the day its all about your roleplaying. But if you need specific value, I suggest 1 POP = 1.000.000 people. This estimation comes from early days of Stellaris, where your starting population was like 8 POPs - current Earth population is 7 or 8 billion people. WIth Le Guin, estimation makes even more sense.Like 1 billion, 2 billions, 5 billions? I want to know just how many freaky aliens I got in my crazy space empire.