Another good episode! (The “Read Poe!” story was adorable) A few thoughts:
I’ve always kind of assumed that Louis XVI was the model for Prospero, but that’s mostly because he was not far removed from Poe’s time. However, Henry VIII would work as a model for an older version. The interesting thing about both of them is that they were second sons. If Prospero became king because the Red Death killed his older brother instead of his father, that would go a long way to explaining why he was so freaked out and why he was so ill prepared to be king.
In the early months of the Covid pandemic, cities were overwhelmed while rural areas were largely untouched – and that’s with 21st century transportation. So, I don’t believe that the 50% number tells us much. It could easily be that 90% of the people in cities were dead.
I’m including a link that tells the story of Eyam, England, because it describes how they were able to get food even though they were in quarantine. If you don’t know the story it’s the mirror image of this story. In 1665, the Bubonic Plague came to Eyam. This villagers isolated themselves to protect the neighboring villages. Many of them died, but the plague did not spread. FWIW: I know someone who grew up about 10 miles outside of Eyam – this is not an Internet hoax. https://www.mentalfloss.com/article/652711/eyam-england-bubonic-plague-village
I don’t think we can say whether children were in the castle or not. They could have easily been in a different part of the castle being attended by wet nurses, nannies, tutors, etc. Or they could have been left at home. Modern rich people do both.
Re the number of people in the castle: I find it hard to believe that people of this class would travel without servants. At a bare minimum there would be one attendant for every man and woman, and probably more. So, 1000 revelers implies, at the very least, 3000 people, and then there are the servants of the castle, entertainers, possible children, etc. I’m thinking it is more like 4000-5000 people.
Louis Pasteur was just beginning his experiments in the 1840s. There’s no way Poe would have known about the germ theory of disease, but, as you said, it really doesn’t matter for the story. That being said, people of the time were working out how disease spread even if they didn’t understand why.