It is generally not recommended to smoke a turkey that large at 250, since it needs to get to an internal temperature of 140 within 4 hours for food safety. However, if you butterfly the turkey (or completely separate it into two halves), and place it bone side down on the rack, you will most likely get to 140 before 4 hours. If at 3-1/2 hours you have not reached 140, then put it into a 375 oven to reach 140, then turn down to 325 until 165 in the breast. It will still be plenty smoky. You can also smoke your turkey whole for 3 hours, then transfer to a 375-400 oven to reach 140, then turn down to 325 until until 165 in the breast. I don't think you are ever going to get "great" skin if you are smoking your turkey. The smoking process slowly renders out a lot of the fat in the skin, turning it kind of thin and papery. You can crisp it in a hot oven, but you might still be disappointed in the skin. It's a trade-off. I would highly recommend brining your turkey. The cooking process and moistness will be much more forgiving. Not sure about the timing. It would depend on whether you split it (faster) and what temperature you finish it in the oven. You might have to be flexible in your eat time for a turkey that large, with a multi-step process. I would guess somewhere around 5-6 hours?
