I've smoked two turkeys. Practice on a whole chicken to get it right. I bought a turkey holder that holds a turkey in the same position as a beer can chicken. I like it and bought it at Cabelas.
I like the hotter cooks, 325F-350F, as it crisps the skin better (I don't lke rubbery skin). Never cooked one as large as yours.....mine have been around 15lb birds. The breast cooks faster so if you cook in the normal position (breast down) then you may want to ice down the breast before putting it on the smoker so it gets done around the same time as the thigh.
Do a search and there are a lot of good suggestons for brining, rubs, etc. Just pull when the thigh is around 160F-165F as you don't want to dry the meat out. It will be good!
OK Joe Vertical Smoker, UDS, Komado Acorn, Weber Kettle Ranch, Weber Kettle, Stok Kettle