Where you get it is totally up to you; there's nothing wrong with going to your local Market Basket and picking up a random frozen bird. If you like, you can also go to a local butchershop with fresh turkeys sourced from New England; or anything in between.

I would aim for roughly 1lbs of turkey per person that will be attending.

No need for a test run, just following some Youtube instructions closely on day of and you'll probably be fine.