In your point-by-point summary page there is a mistake in Beitzah 5a, part 1) letter (f). You write
>>"The two days of Rosh Hashanah remained as they always were, Sefeikah d'Yoma, in Chutz La'Aretz..."<<
But the whole point of the Gemara there is to say that it is NOT a Sefeikah d'Yoma in Chutz La'Aretz, rather it's Kedusha Achas from Takanas Chachomim. See Rashi there.
Feivi Arnstein, Beitar, E"Y
Yes, I think you are right, Feivi.
Rashi DH mi'Takanas does write that the faraway places keep 2 days because of the Safek, because they do not know if day 30 or day 31 became Rosh Chodesh, but that Rashi is referring to places in Eretz Yisrael distant from the Beis ha'Va'ad, while Rashi DH Ha writes that in Chutz la'Aretz the reason why 2 days are observed is because of the original Takanah of 2 days, which was never annulled, and therefore in Chutz la'Aretz the reason why 2 days are kept is because of the Takanah, not because of the Safek.
Yasher Ko'ach for your correction,