When you up the abv you often should up the bitterness to balance the beer. The amount of dme you added probably won't make that much a difference just for future reference.
With that said, I would dry hop with 2-4 onces of a aroma hop (assuming you followed the bb directions and did a 5 gallon batch). The dry hop/s you choose are really up too you but cascade is pretty popular among several others. Most of the time the more dry hops the greater the aroma but this is not always the case and dry hopping can cause haziness.
If you have a bucket put the whole hops in a bag with glass marbles. If you have a carboy drop the whole hops in without a bag and rack on top.
But I've brewed the bb IPA and think dry hopping it is the way to go.
