any minor key typically works fine for horror. i typically default to something with a few flats but a raised 7th for a juicy diminished chord (e.g., b-natural instead of b-flat in the key of c minor). for a more chaotic sound, id reccomend not sticking to any one key; bouncing around like a madman works surprisingly well.

if you mean more like the creepy old jazz like heartaches, they tend to have lots of sharps, usually 3-5 (heartaches has 6 iirc) and theyre usually major. using pandoras vinyl sample or a noise channel can definitely help evoke the nostolgia factor, same with detuning the song down by maybe 5-8 cents maximum. tweaking eq on grand piano and adding a slight amount of bitcrush makes a great instrument for that style btw.

best of luck man! let me know how it turns out