I think this would be pretty tasty!
I love porters & dark brown's, and this is leaning towards the robust porter style with the black patent malt & choclate malts. The IBU's should be good for all that roasty malty goodness. I guess that just depends on how you like your brews.
If you are doing a partial boil (3 - 3.5 gallon boil) your hop utilization should be lower and not look as scary as if you used the 2oz Cascade in a full boil (6+ gallons).
Dry hopping should only add to aroma .. no bitterness .. so add an ounce or two if you want
RDWHAHB ... should be great!