Hold down Ctrl-Shift-C and type "TestingCheatsEnabled true". Shift-click your mailbox and press "Make me some friends". Eventually there will be a vampire.
When you are a werewolf you are resistant to all diseases, but with the Dawnguard DLC you have the option to become a vampire, however you won't be a werewolf...
No, they will usually give you a chance to cure yourself from the vampirism curse and give you a couple of days to do so before they start attacking you.
My best guess is that the pebbles and brick contain limestone, which is easily dissolved in water and will raise the pH of the soil. You'll have to water with...
Nope. Sims appear to have infinite plasma/blood which could be so that vampires have an easy way to replenish the thirst need or so that Sims couldn't accidentally be killed.