My wife and I successfully summited on Sept 23 in both 2011 and 2016, so I have some insight for questions 1 and 2.
Regarding weather: EXPECT ANYTHING. We were very lucky to have completely clear, calm weather for our overnight trip in both years. Others, hiking on directly adjacent calendar days were not so lucky. In 2011, the summit was enveloped in clouds the day after we got off the mountain. I'm sure there were flurries on the summit. In 2016, 9/21 was a horrendous day on the mountain. *Multiple* returning parties we passed on the way up reported that winds destroyed their tents at Trail Camp overnight. 2011 temps were reasonable: cold at night, but only needed long sleeves and a windbreaker on the summit. 2016 temps on both days were absolutely frigid. The night of 9/22/16 was the coldest night I've ever experienced - my thermometer read close to zero F at Trail Camp. Our water froze solid even when kept in our tent directly next to our sleeping bags. I wore six (!) layers on my torso up to the summit, and only stripped to four on the way down.
Regarding the switchbacks, 2011 was a bigger snow year, and is probably a decent proxy for 2017. I recall no issues with snow, and my pictures show very small snowy patches, only near the cables. They were easily passed, along with the ice that forms there that time of year. If 2011 is a proxy, expect a snowbank that you'll need to cross - easily without crampons or spikes - in the last 1/4 mile before the summit.
We didn't dayhike, so can't comment on question 3.
Regarding acclimatization, others here will likely recommend camping at Horseshoe Meadows, at about 10,000 feet, and accessed off a long side road off the Whitney Portal Road. I haven't done so, but that seems to be the standard recommendation on this board if you're acclimatizing near Lone Pine. You mention a "4-5 hour" stay. That won't help much at all, especially if its during the day. If you're coming in on the 15th, sounds like you have a lot more time to acclimate than 4-5 hours, but are choosing to sleep in Lone Pine. Don't. At less than 4k elevation, it won't help much. Sleep higher - much higher. You're coming from the Bay Area. If you're not able to camp, consider a couple of nights along the way at one of the lodging options near the Mosquito Flat trailhead at alomost 10,000 feet. We like the cabins at Rock Creek Lodge and the dayhiking options up to 11,000 and 12,000 feet in Little Lakes Valley are spectacular. There are higher elevation lodging options near Mammoth as well.
Best of luck!
Edited by Steve C (07/10/17 11:10 PM)
Edit Reason: Cottonwood Lakes -> Horseshoe Meadows