Neither one of those hops are normally used for bittering.
I would save the cascade for the end of the boil. I have a really good stout recipe that calls for 1 oz at 15 minutes and 1oz at 1 min.
But you're going to need some bittering hops. You *can* use flavor/aroma hops for bittering, but since they have a lower AA%, you would need to use a lot more of them. However, since the recipe you're using only has 30 IBU's, it doesn't really matter as much as it would if you were brewing an IPA.