Merry Christmas - Happy Birthday!
That's a great gift for yourself. My 18.5 WSM was a happy birthday for me in '09. You already know how to BBQ so you should come up to speed on this pretty quick.
My only suggestion is if you are going for low heat cooks, go ahead and put some water in the pan until you get the hang of temperature control (and until the smoke coating inside the cooker helps to seal it up.) Many more experienced cooks use a clay saucer or just foil line the pan but water is a nice crutch to get you started easy.
Good luck with it.