If you are brining the bird brine it 2 days in advance. 4-6 hours should do fine. Then, pat the bird dry, put in on a wire rack on a plate or cutting board, and let it sit, uncovered, in the fridge for 1-2 days. The skin will dry out and start to look opaque, but this is the way to get supremely crispy skin (unless you have a rotisserie, then it doesn't matter). Spray or rub with a little oil or butter before cooking.
When I spatchcock birds I put the charoal baskets at about 10 and 2 (if you are looking at a clock) and the bird at 6 with the legs facing towards the heat. If you do the bird on a vertical roaster, cook it on the charcoal grate (not on the cooking grate) with the coals off to one side and the bird on the other. If you roast it whole, set up the baskets on each side and put the bird in the middle.
Good luck!