Great idea for beer! Looking at your recipe the first thing I notice is unnecessarily fussy combination of roast malts. Personally I would go 4% roast barley and 8% pale chocolate.
I would also suggest changing the crystal 120 to special B it's more fruity and will give you the chocolate flavor in combination with roast malts.
The orangy hops that spring to mind are summit but I personally would be tempted to go low for flavor/aroma additions and rely on just the orange peel addition.
Also have you considered rye malt? In my mind rye and orange is great combo.
