The amber DME is weird, as you have crystal malt already in the grainbill, so you're effectively doubling up on the crystal malt. I'd use light DME and forget the amber.
I dislike fermented brown sugar, and it thins the body of the beer, so I would leave that out completely and replace it with extract. I can't think of anything good that brown sugar would bring to a robust porter. It should be a complex, roasty beer. Brown sugar is a simple sugar with a hint of molasses flavor that will ferment out completely, leaving a thinner drier mouthfeel behind.
I'd probably go with 1/2 pound of black patent (it's very acrid and astringent), leave out the biscuit malt (very dry in the finish), and cut out one of the 60 minute hops.
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