As to your question regarding Selene and the knife wound - we have no idea what Lucien had on the blade. With the UV bullets - he could have had his blade coated with something which stopped the regeneration process in a vampire - thus resulting in them bleeding to death. Remember, he gave Michael an enzyme which kept him from transforming into a Werewolf, so that sort of bio-knowledge was obviously not beyond them.
I can't remember what the deal is with vampires and running water.
I do know that part of the vampiric myth changes depending upon who is writing the story. In each retelling people find the need to make their vampires more "unique" than the other myths and so they add their own twists to the myth. That's probably why they could see their reflection? I'm not sure. I do know that the closer you are to the original vampire, the stronger you are because the disease is less diluted and therefore less things effect you.
Shawn