What rules would a vampire you created follow?

well, since you're writing about a character that has a "pre-determined" characteristics already, i suggest that you don't go too far from what the people are used to but still add a little bit of spice or something different to the character....well, basically because they need to connect to the vampire that you are creating and at the same time, they need to see a different side to it so that they would be interested to continue on reading....

so aside from the fact that you're vampires need blood to stay alive, you need to think of different characteristics that would make your vampire different from the other vampires that has been written in history...maybe you could make your vampire a very modern person who tests his victim's blood first before drinking it or things like that....it really depends on the flow of your story.

Wow Writing about vampires...

have you ever though that they might have different classes and ranks of vampires... like the most insane ones would be the lower class... and the one who are more noble and could control their fest for blood would be the upper class...
(In this case they fest the blood of their important ones like their lover but not turning them into vampires or killing them...because they need breed with them alive and create a generation of stronger immunity and have more different variety taste of food)
And in this upper class there are possibility in them a group of vampire slayers to kill the lower uncontrollable pest who fest for fresh blood (killing innocent people)...

And Lastly the idea of the next vampire lord to be totally human...

I'm a big fan of paranormal romance novels, and one of the common type of heroes would be vampires. There are so many takes out there for these type of breed, that you can virtually create your own world.

My favorite would be JR Ward's Black Dagger Brotherhood, where her vampires is a separate breed co-existing with humans. I also like Christine Feehan's Carpathians, immortals that drink blood, but has to resist darkness or they turn into vampires. Laurell K. Hamilton's Anita Blake's modern world populate with preternatural beings is another good book.

Again, there is no limit to what you can create. Just remember, the more fantastic the world, the more logical and realistic the behavior should be.

Good luck to your writing!

Think about the old ways. If you have "Ancient Ones", created before Christianity, then the cross and other Holy symbols would do nothing. They have no meaning for one who didn't have that faith as a mortal.