Cherry flavoring addition

Hi all. I am seeking some advise on adding fruit flavors since I have never used them before, I am seeking a starting point on how much to add from those with more experience. I have a Dunkelweizenbock and it has been suggested to add some cherry to it. It sounds intriguing to me. I am looking to get an underlying flavor, similar to that of Sam's cherry wheat. I have listed the main ingredients based on a 6 gal. batch getting about 64% total efficiency. Any advise would be greatly appreciated.
4lbs, Vienna Malt
8 oz. Midnight Wheat
6 lbs. Wheat Malt Extract
1 oz. Hallertauer Hersbrucker -60 min.
1 oz. Hallertauer Hersbrucker -50 min.
.5 oz Centennial -10 min.
White Labs Hefeweizen IV WLP 380

You might try dosing a 12-oz beer and scaling up the amount you like in that one beer. 

My friend that does this well usually undershoots the cherry extract addition at the end of the boil, and then adjusts it to taste when kegging.  You cannot undo it if you go too far.  And use high-quality extract/flavorings.  The cheaper stuff tastes cheaper. 

Hey, I have some question about fruit beer , in particular Belgian beer. What is the amount of fruit flavor I should use? Is it better juice or actual fruit?