Jackbv, I hiked the entire trail last week in hiking boots using hiking poles. In three weeks what little snow is left should be easily walkable. But if you have any fear of walking on icy surfaces, take microspikes. Weather could be warm enough to be T-shirt weather. Or it could be windy and really chilly. Take layers so you can be prepared. When I was there, it was chilly and windy, and two layers was all I needed. I had a thin down jacket in my pack but never needed it.
For acclimatization, sleeping two nights above 8000' is helpful. You can get a room at Mammoth Mtn Inn at 9k. Or you can sleep in the walk-in campgrounds at Horseshoe Meadows and Whitney Portal.