There is Gothic Literary Horror conventions, which are often baroque convolutions of secrets and revelations. And then there is Gothic Aesthetic Horror conventions, which are often baroque paeans to past macabre grandeur. Ravenloft rpg and Hammer Horror films do both, but mainly the latter as it is easier to pull off.
Focus there.
The challenge with the early- and mid- medieval is a lot of our familiar concepts of "secrets & revelations" are tied closer to our time's world view. So our aesthetics & morality are closer to Gothic Lit. foundations because Gothic Lit. is derived from a horror upon collective self-reflection of our past mired in Monarchic Supremacy, Neoclassical, & Romantic cultural movements. The truly medieval is more collectivist in its transitionary period from the personal salvation standpoint into the Renaissance's refocus upon humanism... and the subsequent list of movements above.
Basically neither you nor your audience/players will recognize the truly medieval world view, let alone grasp or explore its existential fear, in a manner that will resonate with emotional satisfaction.
So don't sweat it.
What you should focus on is the Gothic Aesthetics, which is quite doable.
And the best advice for that is Gothic is: a lovingly morbid reflection upon the past, accepting its high contrasts conflated into a breathtaking whole. Beautiful highs, beguiling lows, all part of an unbearable dying reality.
For that you'd have to relook at the medieval, in books, poetry, food, and song... as films do it complete injustice. Add in your loves, like Roman Baths, Pagan Festivals, and Bucolic Farmsteads to high contrast horrors like Plague Scourges, Crusader Wars, and Viking Raids. The secret is passionate outrageous highs and lows, and that is easiest to do about things you care about.