For every influence Hussie wore on her sleeve there's one she pretended to have never heard of. But like, that's kind of just how writing works. It's exceedingly difficult to not be influenced by something you've read before. Even if the only thing you get out of it is "wow that really sucked." Anyways:

Mark Twain. One of the only people in history who earned the job title "humorist." Man knew how to put the spin in a yarn, and there's a direct parallel of him that fucks The Condesce. I will give particular notice to The Mysterious Stranger, an unfinished novel about the devil's nephew.

Dead Souls by Nikolai Gogol. Also went unfinished. It revolves around a man who is buying the contracts of dead farm workers (read: legal slaves) from landowners in imperial Russia. The background of Act 6 involves amassing a ghost army. If you're wondering, Hussie pulled a poem about horses from it.

Insane Clown Posse. Yeah really. Honestly you should take a rap tour in general but let's start with the one literally in Homestuck. I'm not telling you to binge the discography, but look around. How ICP responded to the culture around them in their work and wound up creating their own subculture because of it is a blueprint for the ways Hussie criticizes general society in Homestuck. The real Dark Carnival is a series of concept albums describing the weird and crazy belief system of ICP and their fans. Which turns out to be Christianity. I am neither exaggerating nor interpolating here. I mean there are non-christian juggalos; it's not like an actual sect thing.

Like a general wikipedia dive on some of the named esoteric stuff would help you. I know enough about say, western alchemy or gnosticism to not be confident in recommending a specific text to read on either of them.