All I have to contribute is add the chamomile at the end of the boil, like with 5 minutes left. Chamomile doesn't weigh much, so you'll need a scale that can measure grams.
Not sure if grapefruit juice is such a great idea. The hops should take care of bitter and citrus-like flavors. You can add zest, though (at the same time as the chamomile). Look at wit recipes that use chamomile, zest, and coriander to get an idea.... IPA is a stronger taste but don't overdo the adjuncts.. much safer and more drinkable to under do it.