How did Humans on Earth become such a perfect society?
We're not, it's all tourism propaganda to bring in imnterstellar vacation travelers.
How did the world respond to the news that aliens had arrived?
At first they ignored it, thinking it was nothing but another Roswell 1947 thing. It didn't help when the National Enquirer were the ones to break the story first.
Were there religious revivals, xenophobic campaigns, conspiracy theories about... well, just about everything?
With the knowledge that life exist elsewhere (everywhere) there would be a surge in Religion.
They come across a warp capable civilization that was in a post-apocalyptic state with waring factions killing off their own kind.
The Vulcans thought ... wow, they're just like us.