I have done Whitney four times - once as a dayhike from Portal, once as an overnight from Portal, once on a five day trip around to the back side from Horseshoe Meadow, and once from the west side of the Sierras on an eight day trip, starting at Marvin Pass, going over Colby Pass to meet the High Sierra Trail at Junction Meadow.
Despite the crowds, it is a hike that everyone must do at least once.
I'm assuming your permit is for the dayhike. It's a long long day - 22 miles with over 6000' vertical up and then back down, and you start at 8300'.
There are a lot of people on the mountain, and my biggest problem was the presence of excrement under every rock in the Trail Camp area (at 12,000'). Be careful where you get your water. I would fill up at Outpost Camp, either at the small creek that comes in from the south before you get to Outpost, or at the stream on the north edge of Outpost (the stream that comes down from Mirror Lake). I would not take water from the main stream draining Trail Camp, which comes over the waterfall at Outpost Camp. Another good place to get water is on the switchbacks above Trail Camp, there is a snowmelt flow that crosses the switchbacks several times.
Start early, around 3AM, so you can summit early before any real danger of thunderstorms develops. Sleep high the night before, and if possible take a few hikes at elevation in the days beforehand. If you can't get a campsite at Portal, camp at Cottonwood Lakes or Horseshoe Meadows, where you can also do some nice warmup hikes at elevation.
Stay hydrated, and don't carry a lot of unnecessary weight. Good footwear is important. Sunscreen is a good idea.
When I did it as a dayhike from Portal, on the way down I kept thinking that I didn't remember it being so far.
And, contrary to almost all sources, the official USGS elevation of Whitney is 14,505'.
When will you be there? I will be going with a scout troop on a six day trip to Whitney starting at Onion Valley (Kearsarge Pass) during the first week of August.
Both times I have approached the summit from the west side, I have been on top by 8:30 or 9 AM, and there were only a few others on top. The crowd from Portal starts arriving around 9:30 AM. If you start at 12:01 AM on the day of your permit, you can be on top for sunrise and have it pretty much to yourself. Then you will pass the crowds on the way back down.