gmonkey wrote:(long story short: let's just say my idiot cousins did the turkey last year in an oven bag and decided to just dump a bottle of Italian dressing in and call it a day).
Yuck.
Gmonkey, welcome to the world of roasting a turkey, a world where there are more theories as how to "properly" roast a bird than there are about where the second shooter was in relation to JFK.
In short, there are a lot of techniques, but none are absolutely correct.
gmonkey wrote:Here are my questions:
a) I know brining is recommended, but with the butter do I still have to do that?
You never
have to brine. I brined for the first time last year and thought that it made the meat too mealy and too salty. I'll make adjustments this year for experiment's sake, but the object of brining is to (1) add some underlying flavor to the bird by adding spices/herbs to the brine itself; and (2) act an an insurance policy against the bird drying out. I find that with other measures, such as proper timing and basting (which your porcini butter will do), your bird won't dry out. Use of an instant read thermometer or probe will help you gauge the doneness of the bird so that it doesn't dry out. [If your Mom was like mine, she probably put a fine bird in at 9 am, and removed a dry one at 4, the only guide to cooking time being her gut, and she didn't even
know what a meat thermometer was, much less used one.]
gmonkey wrote:b) Does it matter if I roast the bird breast side down?
Again, another theory, grounded in the idea that the breast will "self-baste" while it's upside down. Because it's only one theory, no, it doesn't matter because there are other ways to achieve a moist breast (okay, this is getting a little embarassing . . .

). One way is to baste, another way is to put the butter under the skin (make sure you're liberal with it - in fact, I'd taste the porcini butter for strength, and if it's pungent, I'd use a mix of porcini butter and regular, unsalted butter so that you have enough butter to baste the breast and the porcini doesn't overwhelm).
gmonkey wrote:c) Can I employ all three of these methods (brining, subcuteanous butter and breast down cooking) and have a successful, moist, flavorful bird?
Yes. But I'd be judicious about adding additional herbs and/or spices to the brine so as not to overwhelm the flavor of the porcini butter. (Or add only herbs that will enhance the porcini.)
gmonkey wrote:d) Do I really need a V-rack to roast or can I just lay down a bunch of vegetables under the bird?
No, you do not need a V-rack. It can sit on vegetables, but cut them thick (so they don't cook down and flatten out) and evenly, so that the bird sits evenly in the pan. I always put the bird on veggies that will later flavor my drippings.
You'll get a ton of different answers, I'm sure, but I hope this helps!