Excellent post, thank you for sharing this.
In an answer to your question: The stairway hall is probably my favorite room I think. But to be honest, It's hard for me to pick a favorite room from the photos as they're all very ornate and intricate. I LOVE the dome of the tower room though, and that would probably be where I'd want to spend the most time if I lived there.
I was really impressed by the kitchen though. The old stove range and ovens are amazing, and the hood above them almost looks modern/recent. I didn't see mention of what era the house was built, but I'd guess maybe late 1800's early 1900's.

I've always had an infatuation with elaborate stairwells in large homes, and since a kid I've always been obsessed with mansions and castles.
One movie stands out to me that might of started this called Casper (from 1995, I was 6 years old). The house was called Whipstaff, and it was in Maine. It was fictional, but what an amazing design it was. The manor was inspired by my favorite architect Antoni Gaudi's Casa Batllo in Barcelona who also designed the still-unfinished world famous Sagrada Familia Basilica which is also in Barcelona.

Whipstaff:

Casa Batllo:

Interior Batllo:

Casper's Bedroom:

The doorways, windows, ceilings, etc. are all taken straight from Gaudi's Batllo.

The Whipstaff main-hall and staircase was especially amazing though:

And as amazing as those homes are they don't hold a candle to his master work. A Christian basilica with design like no other, and there are plenty of oustanding cathedrals and basilicas. Gaudi took all of his inspiration from nature, and said God's work was his greatest inspiration. when designing the Sagrada Familia he did it upside down with strings and pouches of sand or salt to find the most natural balances for weight distribution.
Work started on the basilica over 130 years ago when Gaudi was still alive, and it's nearly finished with recently started heavy construction. It's sad because you can easily see the difference in the work done under Gaudi vs. the new work:

Detail of the main front-fascia's epic sculptures:

But then there's the interior main hall. The support columns were inspired by trees:

Sorry for turning this comment into such a huge post, but I figured you might also appreciate it. I honestly didn't love architecture until I discovered Gaudi, and oddly enough it was Capser and Whipstaff that led me to it.
Can't wait for part two, by the way.