Concerning the transformation, I liked the idea of a vampire having to drain someone entirely dry of their blood before filling them with vampire blood to start the transformation. So, technically, only a corpse could become a vampire, but it should be fresh enough that the vampire blood can put the body back together. No regeneration power while the transformation is over, too, so falling off a cliff would render transformation hopeless.
Then, about the powers, everything would come down to the blood. Bleeding a vampire dry could technically kill them, staking them too (if the stake stays inside, preventing regeneration). Beheading could work, because you leak from everywhere then, but I guess if you could quickly get the head back and feed it enough vampire blood for long enough they'd be able to regrow their body.
Vampire blood would have the basic power of fastening the healing and changing the body into another form. For example, at the beggining, you'd still be able to eat normal food, but the more time goes by, the more your digestive system strives towards blood instead of food. That would make you need to feed less often. Also, while at the beggining you'd just heal faster and have normal human scars faster, as time goes by your body would retain more information after a wound, eventually allowing you to grow whole organs or limbs back.
Perhaps at some point you'd develop more powerful pheromone glands and the ability to control them, allowing the famous "glamour" of vampires.
I like my vampires low-fantasy and down-to-earth, yes. Stuff like being repelled by the cross, forced to count everything that comes by or magically prevented to enter churches or someone's home without their permission is bullshit to my eyes.