adding your DME at different times is pointless
throw it in at the beginning of the boil, the only tying you are using your DME for is fermentable sugars, and you want those alpha acids isomerized as much as possible with those sugars
and as far as a bigger beer, thats all fine and dandy, i like bigger beers myself, and it should actually come out to around 6% abv if it attenuates properly
i dont remember off the top of my head what hazlenut brown is, pretty sure its 6.2, but not possitive, so this should work out for you