If possible, Marry a chick from Iowa. I hear their Fathers give them away WITH a pig roaster.
We have done them on rotisserie and that works pretty good but the last half dozen hogs have all been done in smokers. not butterflied.
Apple injections are a must
Slow cooking 155 is also helpful... usually plan on 1 hour per 10 lbs. Plan on having it done a couple hours before you need it as it's easier to slow down the process and keep it hydrated then it is to speed up the process at the end of the cook time. Don't think you are going to be able to increase the heat enough the last two hours to make up for falling asleep half drunked up while on duty.
we always stuff them with something (usually more pork as that's what everyone is there for) but I have to tell you the chicken sound good & I'll try that next time.
If you dice your garlic real fine and add some other rubs etc. you can usually get them to go through the injector too.
Ano0ther thing we do is add a water pan at the source of the heat..I'll fill that with a little of everything... Tequila, orange and lemon juice as well as the peals and all... I'll even put apple cider and cut apples in there sometimes... We usually try to use Apple wood for the fire too but make do with what you got. It will be fine.
Cover his snout & ears with foil to keep them from burning off and as far as the skin...I don't know, I always wind up with un eatable skin but hey, the dogs love that and they have to eat too.
One last thing, If you are going to butterfly that bad boy, look on-line for plans to build one out of cinder blocks... you build it on the ground, cover the bottom with sand, put your grate on there and cover the whole thing with Tin Sheeting.. Build a fire at both ends...It looks really nice and when your done you just take the blocks down and stack them at the back of the house. (You don't morter the joints) just stack and go.
Good Luck!