You will first have to change your fairy Sim to a normal Sim using the potent cure elixir or the "ask forsake the fae" action with a significant other, then follow the steps in this tutorial.
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.
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.
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.
