For that sized crowd, I'd choose a 20 to 22 lb. bird. Mkae sure that it's completely thawed. Then remove the giblets and neck from the body cavity and the flap of skin that covers where the neck used to be. Rinse the bird uder cold water and dry inside and out with paper towels. Place the giblets and neck into a 2 quart pot, cover with water, and bring to a simmering boil. cover and let it cook over low heat.
Use that handy plastic legg-hold thingy that is already in the bird to hold the drumstick ends in place. Fill the cavity loosely with stuffing, if you are cooking the stuffing in the bird. Next, fill the neck hole with stiffing and sew the neck skin to the brest with white, pure cotton thread. Again wipe the bird down with a paper towel. At this point, you can do all kinds of things with the bird. You can stuff rosemay leaves under the skin, or a compound herb butter unter the skin, or you can just rub oil or butter all over the outside of the bird. I take about 2 cups of the turkey broth from the boiling sauce pan, let it cool and season it with salt, pepper, and sage to taste, then inject it all over the breast, in the thighs, and into the drumsticks. Fold the wing tips under the back and place the turkey on a rack, and into a shallow roasting pan. My oven is preheated to 450' F. I place a meat thermometer in the thickest part of the breast, taking care not to let the tip touch any bone. Put the bird into the oven and let it roast for 15 minutes. I then turn down the heat to 400, loosely cover the breast with a tent of aluminum foil, shiny side out, and put it back into the oven. I roast it for about 12 minutes per pound. When the time goes off, I check the meat thermometer. It's usually reading about 145 by then. I baste the bird with pan juices to get some of that flavor on the skin. Know that basting doesn't make the meat any juicier. It just rolls off the skin after depositing some flavor solids onto it. Remove the tent and place back into the oven. Roast for 15 minutes more and check the thermometer, again baisting. REmove the turkey when the meat thermometr reads 155' F. Let it sit on the counter for twenty minutes. Teh final temperature will read 165' F., which is perfect.
Remove the stuffing, front and back. Cut off the whole legs at the hip joint. Remove the wings at the body joint. Cut the hwole breasts off of the bird by sliding the knife downward, along the breast bone. Slice the breast meat against the grain so that every piece has some of that crispy skin. Place the breast slices on a large platter so that they resemble the unsliced breasts, and surround with the legs, which have been seperated at the knee, and the wings. Place the stuffing into serving bowls. Make gravy from the remaining meat juices, both from the roasting pan, the cutting board, and the pot.
This will make the most tender and juicy turkey you have ever eaten, becuse you removed the bird at 155' F.
I have barbecued my turkeys over charcoal, roasted at 325, at 290, at 450, at 375, and the way I described above. In every case, when the bird was removed from the heat at 155, the turkey was incredible. Cook it to a higher temperature and the meat begins to toughen and dry out. If you wait until that little pop-up timer goes off, the meat is so overcooked that it's like eating compressed sawdust.
There are others here who have differing methods for preparing a turkey, and each swear by their own methods. Cooking in a bag steams the bird. Deep frying transferes heat very quickly to the meat and results in wonderfully crisp skin. It also shortens cooking time, as does cooking over a devided bed of charcoal on a covered kettle grill. But no matter how you cook it, if you take it off of the heat when the meat temperature reads 155, your bird will be better.
Oh, and one more thing. On the back of the bird, just behind where leg joins the body, you will find a chunk of meat on either side of the back, in a little hollow. These are called the oysters and are the best meat on the bird. They are bite-sized pieces. Call your favorite someone, be it one of you children, or you spouse, or best friend, favorite uncle, or... well, you get the picture, into the kitchen and share one of the oysters with them. It's a great little tradition that makes that person feel very special indeed.
Seeeeeeya; Goodweed of the North