Why the gypsum? If it's to enhance hops, that may or may not be the correct thing to do, depending on your recipe. I'd leave it out unless you are confident of your water profile.
The extra nugget hops will make the beer 50% more bitter. If you like a very very bitter beer, that might work. I wouldn't, as I think it would go against the wonderful roast of the original recipe.
I don't know what the projected OG of the beer is, but with an extra pound of DME and a pound of brown sugar it won't be the same beer. I personally hate the taste of brown sugar once it's fermented, as the sweetness is gone but it leaves behind a weird molasses flavor, but I think some people like it.
I don't know about cocoa, so I'll have to let someone else answer to that.
I actually like the original recipe much better than the improvements, but if you really want a bourbon chocolate stout, you can try using cocoa nibs and soaking them in bourbon first to give you a good flavor without using the cocoa powder.