I've only used strawberries once, and found that the flavor fell off quickly. It's been more than 15 years, so I don't recall how much I used. If you want a strong flavor, I would use puree and supplement with extract in the keg to bring out the aroma. If you do just extract it will probably taste artificial, I had a beer like that a few years back and it was awful. Expect renewed fermentation when you add the fruit, I would probably hold off on the nibs until that is done. And I would go with at least a pound of fruit per gallon.