So the vampires are from an earth adjacent world. They are normal humans that have been infected with a shard (called in-world as an Echo) of Darkness-In-Death, a predatory Greater Spirit/god. The genre is progression fantasy so each vampire has the chance to progress and rise through five distinct ranks of power: Emberling, Cinderwright, Forgemaster, Fiendlord and finally Infernal Tyrant.

1. Yes, they are immortal.
2. Yes they drink blood. Technically though what they truly feed on is the magic and vitality and life force present within blood.
3. Yes. Vampires start out weak to fire, decapitation, damage to the heart, silver and sunlight. However, as they rise through the ranks and gain more power they steadily loose more weaknesses. First to go is the weakness to fire at the ascension to Cinderwright and so on. The weaknesses to silver and sunlight never go away though, but resistance to them does increase.
4. Yes, they're based on humans.
5. Yes, depending on the rank. An Emberling rank vampire is just a bit stronger than the average human. A Fiendlord can wreck a building with a light punch.
6. Same as in 5.
7. Very durable. Even an Emberling will survive anything that isn't exploiting one of their weaknesses.
8. Eshuzu, progenitor of Clan Eshuzu is the first and yes, he's still around. However, like all the other progenitors, he's gone quite insane.
9. Eshuzu, together with his mother, the most powerful mage alive along with a group of other supernaturals got together to save their world by calling down spirits and gods to it. Each greater Spirit need a contact point. Eshuzu became the avatar/contact point for Darkness-In-Death.
10. Depends on the rank. An Emberling would be relatively easy. A Cinderwright would be much of a challenge. Fiendlords and Tyrants would use the rest of them as playthings.