Vampires Questions

Vampires are in popular culture a lot lately. This is nothing new as vampire myths are found in nearly all cultures. They take many different forms in world myths, and in various popular fiction. However, there are a few basic questions that never seem to get answered about them.

The need to consume blood is an extremely common theme with vampires. How much blood does a vampire need daily? Is a pint enough? Or do they need several gallons a day? Does it need to be human blood? Would pig, or cow blood work? What is it in the blood they need? Is it just the red cells, or is the plasma needed in the vampire diet? Or is it just the iron and water that are in blood? Could supplements be a substitute for the blood? Is it only blood that can satisfy a vampire? Could they use the marrow? Or any other bodily fluids for that matter?

Generally speaking vampires have fangs. These usually look like nothing more than enlarged canine teeth, but what are they really? Are they like hypodermic needles that extract the blood? Or are they just sharp teeth that make a hole that the blood is licked from (like a large feline)? Are the fangs really necessary in modern vampires? The lower teeth a vampire don't seem to have a place built in for the fangs to go, so how does a vampire close their mouth? Do the fangs retract? Also, do the fangs need sharpened ever?

Why is it modern vampires are so sexually over charged? What happened to the "Nosferatu" style of vampire? Predators are not sexual attractive to their prey. Gazelle don't want to fuck lions, nor do rabbits want to bang wolves. Having sex with your food just seems like a bad idea.

Also, modern vampires don't seem to act alone anymore. There seems to be a trend of vampires having a large secret society in modern fiction. Why don't they work alone anymore? Dracula worked alone, seemed like it was going good for him.  While there are pack hunters, most predators work alone. Do they really need blood in such amounts that they need to band together to ensure a regular supply?

Now vampires do have a lot of weaknesses that generally would get in the way of normal life. Sunlight comes to mind. Since the sun is a problem, how do they do thing that need to be done in the day? How does a vampire handle jury duty, or going to the DMV? They might be feeding on people, but they still need to somehow hide within the society they are finding prey in. For that matter, how do they take a drug test for a job, or pass a physical? How do they explain the lack of aging to the people they must interact with on daily (nightly?) basis?

Anyone have some insight to any of this?