Direct democracies can control 5 more planets directly. We don't yet know anything about tier 2 governments. And I hope there will be technologies giving you the same perk.
1000 stars would mean a 25 stars per per empire average. I'm wondering whether all stars will have habitable planets but if yes by late game it translates to about 30-35 planets per empire as some systems have more than one habitable planet if you divide the galaxy evenly and every single habitable planet gets colonized.
My guess based on the Blorgstream is that somewhere between half and a third of systems have habitable planets. Rounding up slightly to account for systems with two or more inhabitable planets, this means that in 25 systems there will be 8 - 13 habitable planets.
If you're a Direct Democracy then 8 planets can all be personally micro'd. Otherwise, this means your five best planets are your core and there's a remainder of 3 - 8 which form one or two sectors.
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