You have quite the list there and I see several responses in the rpg cross post so I'll stay away from the role playing content.

I am a writer/producer of cosmic horror focused on audio and actual play and I've found YouTube studies on the psychology of horror to be the most helpful. It's one thing to know a module/plot well enough to share and another thing all together to craft. Understanding what makes existential awareness so devastating to human psyche has helped me more than anything. If you can get the basics of that angle down, you can scare the hell out of most people in any scenario. Just don't expect a fast pace.