The last duck I smoked was soaked overnight in buttermilk in a 2 gallon ziploc just to make sure there was no gaminess, then I made a rub from equal amounts of kosher salt and coarse black pepper and rubbed that all over the bird.
I then smoked it for about 4 hours at 225 until it reached an internal temperature of 165 degrees F.
It was super delicious! We basically stood around the kitchen counter and devoured it like a bunch of barbarians
Brining it for 4-5 hours would do it some good and the fat on the taters probably ain't a bad idea either.
My Basic Brine consists of the following:
1 gallon of drinking water
1 cup of kosher salt
3/4 cup of brown sugar
All of this will dissolve in cold water if you stir for about a minute or two.
You can add other things into the brine like hot sauce, soy sauce, worcestershire, beer, wine, fruit juice, etc. to jazz it up as well. If you add things that will not dissolve it will need to be heated on the stove and allowed to simmer on low heat for about 10 minutes or so and then allowed to cool to <40 degrees before adding the duck to the liquid.
Always brine in the fridge or in water that is kept at <40 degrees with ice.
Check out all the other information on duck as well as you might get several other ideas that will help you plan out how you want to do it.