You need to treat fruit additions like making wine from fruit. I will use frozen fruit and mash at pasteurize it at home to save money. The fruit and beer should go into primary together. Add Pectic Enzyme at a rate of 1 table spoon per gallon (helps extract more juice from the fruit), I also add a wine cider yeast alone with my beer yeast. I allow the primary to ferment down to .02 specific gravity from final gravity. Rack the beer and leave the fruit and allow secondary to run for 3 weeks and Final Gravity should be achieved. I then rack again and allow the beer to bulk age for at least 2 months just like you would with wine. I have a blueberry Chocolate Stout recipe located here http://hopville.com/recipe/429989/belgian-dark-strong-ale-recipes/chocolate-blueberry-stout . It uses a lot for fruit, 20 pounds, so it is treated even more like a wine in that it will bulk age for 6 months before kegging. The oak and Chocolate powder goes in when it is bulk aging for 6 month. If you are going to use a lot of fruit you MUST be patient and good things will come to you.