I dunno, seems like you got 3 beer styles going on. Why cocao nibs and roasted almonds? - and why not replicate those flavors with grain and not worry about problems with head retention and other variables. Also, those grist numbers can't be correct; 3oz of carapils isn't going to do anything when you have 20lbs of base malt, same with the crystal and chocolate malts if you are looking for anything but color.
Why not just make a traditional "English" brown ale and know its gonna turn out great for your sister's big day?