Lucky you :) This is one of my favourite packs and I am still finding things out about it. It has such a lot to keep you entertained. The best way of converting a normal sim into a supernatural is to look for a potion. I am reasonably sure there is one for both vampire and werewolf. Your sim can also ask an existing werewolf to turn him by biting him. I have done this once and it is rather creepy. I believe there is a similar thing for vampires but they are not my favourite supernatural and I have never gone out of my way to create one in game.
Each supernatural has some pretty awesome skills so it is worth taking each one in turn to find out the kind of things they can do. One thing you will have to deal with now you have Supernatural installed is the zombies. Each full moon they will appear. They are unlikely to attack your supernaturals but will attack other sims who are silly enough to be outside at a full moon. If you have sims who garden they will need to protect the gardens from zombies because the little blighters will decimate it pretty quickly. The simplest thing is to use fences and lock the gate to everyone but the household. One word of warning zombies can spawn within the protected area so you may need to rethink this strategy. Another alternative is to use the greenhouse from the Store.
Moonlight Falls seems to work relatively well. With Supernatural installed your sims can teletransport and your witches when suitably skilled can ride vacuum cleaners. The world is not as attractive as some but the architecture is lovely (IMO) and you get specific lots for each supernatural type. The fairy garden is definitely worth checking out and the broomstick arena where witches can practice flying and do stunts for tips is great fun.
