Just adding a few items:
Do not rely on the Tesla Trip Planner that is accessed on the touchscreen. It is still wonky, and generally has you raring to go to your next stop with a 5% buffer. Personally, I would never leave with only 5% reserve as too many unforeseen things can arise over your next leg. People on this site have their own personal comfort levels with the amount of buffer they desire before departing. Some will go as low as 8-10%; others generally are more conservative at 15-20%. Instead, input your next charge or your destination each time you stop to charge, and then look at the "trip" tab on the energy screen. This will display a line graph showing current capacity, and estimated capacity at your next stop. It is pretty gosh darn accurate if you drive with the flow of traffic (not exceedingly fast), as it does factor elevation gains and losses into your usage. It does NOT factor in variables like weather and heater/AC usage. Cold weather, rain or snow, headwinds or crosswinds can really chew up your usage. Once you get underway, the trip graph will extrapolate your remaining state of charge based upon your actual driving pattern. You might very well leave X with a 20% reserve to Y and see that reserve drop faster than originally anticipated because you are driving into a headwind, or it is raining hard with a lot of water on the pavement. When you are unsure, you can always start out slower than you would ordinarily drive (say 63-68 MPH instead of 74-78 MPH) and then increase your speed as you feel comfortable with the amount of range remaining vis-a-vis the distance to your next charge.
Next, scout out your charging options on PlugShare or on Tesla's web page. Some of the locations (like Needles) are not the best. Needles has four stations in the parking lot for a Dairy Queen. Two were ICEd when I was there this past May. With a decent charge at Barstow, you would only need about 10-15 minutes at Needles to make Kingman, which is slightly better than Needles. (In other words, if you want to eat, eat at Chili's in Barstow. Use Needles for a pit stop break!)
I am not sure where you will be departing in LA, but you do have some options. You likely could skip Rancho Cucamonga and stop in Barstow first if you left with a range charge from home. But Rancho Cucamonga-->Needles bypassing Barstow is nigh on impossible unless you drove 50. Similarly, I made it with a range charge from Kingman to Barstow (Needles had not been built then) with 38 miles of range remaining by driving 68 in Arizona (all downhill to the Colorado River) and 64 in California until I reached Ludlow, and then I drove 74 into Barstow. There was no wind that day.
I had a panhandler amble up to me in Quartzsite a year ago December! (I was not aware of the locals peddling their wares across the street from Carl's Jr.)
In any event, you will have a blast! Supercharging changed me. I am much more relaxed stopping every 1 1/2 to 2 1/2 hours to stretch, walk around, and do whatever else for that 15-50 minute time period.
