I'd recommend to not get rid of your existing car until after your new Tesla is SITTING IN YOUR DRIVEWAY. Even after having a VIN assigned, there might be issues in actually receiving that car (we've all seen the photos of the semi going under the low bridge and smashing the cars on the upper deck. Ditto the overturned semi).
My understanding is that we can't open the door until we tell the app that we've accepted delivery. So you can check-out the exterior before that, but not the interior nor operations via the interface. There are several ways to open the car on Day 2: card, app, fob, ring. But on Day 1 at delivery, the process is more limited until things are paired up. And you will want to review the manual about how to wave the card around to unlock the door (or practice on your father's). The process will become second nature after doing it 10 times, but on attempt #1 at delivery standing in front of your car in the lot it may seem very frustrating. Just remember, it doesn't have voice commands outside. So yelling at it to open doesn't work
The at-delivery process seems to be hit-or-miss. Some folks report a very positive and helpful experience, others report that they are basically on their own. We all wanted to get rid of the legacy stealerships, so this is a consequence. Just be positive at delivery, assume you'll do everything yourself, and go for it. If someone helps, then that makes the process even better. And it gives you an opportunity to ask them for a free Tesla hat.
Here is the step-by-step sign at the Stockton delivery center:
View attachment 710943
Scott
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MYLR | Red ext | White int | 19" | 5 seats | tow | no FSD | Order 07/31 | Profile 07/31
EDD: January
DC: Stockton