'Tis the traditional greeting of angels to humans, because the original versions were beings of cosmic horror.
In-universe equivalent of "Parisian whore", basically.
Basically a cave deep in the forest, yes.
Also, you are in a fantasy version of the Holy Roman Empire in the equivalent of the early-to-mid 16th Century. I'm stealing certain elements from places like Warhammer Fantasy and Bloodborne and the like. Patriarch vampires are also sort of based on how I would rewrite the Abyssal Exalted to be less 'Solars with black eyeliner' by stealing certain inspirations for design from the Infernals but still letting them be their own thing. The progenitive patriarchs/matriarchs that never had another vampire ruling them are all essentially a form of ghost story and sickness each, which they pass down to those they sire. Dieter is the Wronged Man With Unfinished Business and the Burned Alive Ghost, and thus draws his thematics from those sorts of stories, while also having his own personal flourishes. While he has issues with overconsumption because of his venial sins in life and thus once he starts feeding he kills his victims outright most of the time, his thematics lead to 'consumption by fire', and thus if he could moderate his feeding then minor attacks would manifest as severe fever. Many other vampires have their feeding more like the classical anemia or tuberculosis, but any sort of 'draining' sickness works as symptoms, from dementia and Alzheimer's for slower feeding vampires to cholera-like symptoms for dehydrating attacks or cystic fibrosis for 'drowning' type draining.