Oh wow, this has SO many possibilities!! Is this a story line for a book, or a TTRPG? Either way you have a lot to work with already.
I'm going to brainstorm here, so pardon my barrage of random text
You could go with the number of rooms being something like 13 or 7, where the number represents something integral to your story line. (Mystical/holy numbers, etc) You could throw a morgue room in there since, well....necromancers and all. What about Monks? Would they fit in somehow? Torture dungeon in the basement. Malignant Spirits. Halfling creatures......Half human - half gelatinous slime creature.....etc. Lobotomy room! Famorians? Tieflings? Deitys? oh my! Dragons? You could add a cafeteria area, as sanatoriums would have. Storage closet with a secret door leading to a maze/dungeon etc.
Okay, I think I'm done for now. hahaha....
As far as where to get ideas...I am a huge fan of D&D (sadly I've never had a chance to play but I binge watch other fellow nerds play it on you tube) and there are some great free resources out there. Look into NPC's and characters as well as ideas for backstories. I'd love to know more about your project. Good luck!