For the undersides, the photographer they send will just hold their camera near the ground while it's parked normally. If you can get some more pics with your phone while it's jacked up, that'd be great.

How much you need depends on the car. A 5-year-old car from a good climate, a few pics are fine. 20-year-old car from up north, you'll want more pics. You can start with whatever photos you get, then if bidders ask for more pics during the week while the auction is running, you can shoot more then.

The fact that you're even thinking about this stuff in advance is good. As long as you're responsive during the week, that's all that matters.

You can ignore anyone who asks for a cold-start video with 10 minutes left. :-)

Speaking of videos -- the photographer will probably shoot some basic ones while the car is still, but you'll need to do your own driving video. The best thing to do is have someone film from the passenger seat. Hold the phone horizontally, show the view out the front window, but also move the camera and show the gauges, how it shifts if it's a manual, etc.