I highly recomend two things. When you do your two turkeys, get the biggest two that will fit on the smoker. Trust me there will be fights over any leftovers and you'll still want a smoked turkey gumbo or soup too! Don't worry about figuring pounds per person...
Second, Thanksgiving your going to want a presentation bird, I can't recommend enough the use of "Kitchen Bouquet" as a rub before any spiced are put on the outside. It has NO taste you will notice on the bird. It will give you the most beautiful mohogany color on your bird. Kitchen Bouquet is available nearly anywhere as a browning and seasoning sauce. Below is a bird I did with it.
Yes its cheating, yes its easy, My Pop always used it and taught to me as the "Family secret". Try it on your test bird.
I'll leave the brining/injecting/rubing/herbs and spices for everyone to discuss. Everyone has their own favorite way.
BTW I see its your first post, you might run by the ROLL CALL section in the FORUMS so you can get a proper introduction by all the Guru's who will help you get started right here so as to insure your continued enjoyment of the site. I promise its doesn't hurt..... much.