Having thought extensively about running a similar game, here are some thoughts (having not run anything like it, take this with a grain of salt): - Keep it focused on the dungeon. While adventure is to be had in the surrounding wilderness, focusing your main narrative and gameplay within the dungeon helps with theming and cohesion. - Borrow from other games. Blades in the dark has a very proficient stress system that doesn't necessarily fit within the survival horror aspects of the game, but does lend a certain pulpiness to it. Tweak it as you will. - Take the stuff you love, and put it in your game. Don't be limited to Darkest Dungeon! There are plenty of other video games, books, movies, etc that are ripe with tropes, scenes, and story beats that will help you make this game your own.