As a player I have played Vampires before, but I have yet to find a DM who could answer these age-old concerns:
How much blood does a vampire need to drink and how frequently must the vampire drink that amount without suffering negative side effects? Does being a different kind of vampire like a warrior vampire or spellcasting vampire (MM pg 298) affect the amount normally required?
As a DM I would like a reasonable answer to this question; it's something I have wondered about for years.
I'm building a society ruled by vampires where non-vamps must pay a "Blood Tax". You donate X amount of blood either weekly or monthly (haven't decided) and in exchange you are protected from being hunted. This makes the citizens feel safe and secure knowing that they won't be hunted and also saves the vampires the hassle of dealing with all of them hunting in the same area and causing a shortage of prey to feast on. The Hunt is reserved for criminals, rebels, and others who actively break the law of the land and is treated like a sport by the vampires.