The brookies are neither picky nor hard to find; fly selection isn't real critical. A few attractor patterns should be all you need, possibly with a dropper if you're comfortable with one.
They Park has an extraordinary number of rattlesnakes, watch were you put your feet.
If you have hippers, bring them. You don't need them to wade in, but they might offer some protection from the aforementioned critters, and they'll offer protect from something else that the Park seems to have in abundance, stinging nettle.
Rod length is a personal preference, but I usually use 6 footer in the Park, and keep the leader fairly short. Expect to lose flies.
If you're hiking down from the top, the speed limit along Skyline Drive is 25 or 30 (can't remember which, and there will probably be people going that speed, so you can't go faster even if you don't care about the law. (Not to mention that even at that speed, I've come within inches of hitting a bear as I came around a corner the last time I was there.) Expect it to take longer to get anywhere then you think it should.
Give yourself plenty of time to hike out in the evening, unless you've got a permit to camp along the stream.
Enjoy yourself.