Shifting into Low doesn't try to keep a constant speed, the hill descent control does. Personally, I'd rather keep it in L and manage the speed with the accelerator pedal.
I *think* that the loopy arrow over the battery display on the left screen is only shown when friction braking is applied, but I'm not sure about that.
When you plug the charger back in, the car wakes up and checks stuff; it will go back to sleep when it's satisfied.
The indicator on the lower right lights when the doors are locked. Yes, it should be a button, but it isn't.
I consider it a bug that the car doesn't keep the 12v battery topped up when plugged in. If I'm going to leave my car undriven for long periods, or in cold snaps like this, I use the fob to start it occasionally, just to try to take care of the 12v.
I suspect that they used those beefy cables to attach the battery because that wouldn't require a special part.
At the end of each trip, the left screen briefly shows per-trip stats, including how much regen you get; I typically get about 20%.
Folklore indicates that the high-voltage battery will last longer if you keep acceleration low, and use EV Later if you're going over 45mph. My 2013 Energi still has 20 miles in the HVB, so I tend to believe that. I use EV Later whenever I'm going farther than one exit on the highway, or when there are hills to be climbed; my town is sliced by a highway, it's damned convenient to use it to get to the other side of town, and I'll use the HVB for that distance.