If you plan to drive your REx on trips that exceed the EV range, where speeds exceed 70 mph, or which include long inclines at highway speeds, you should consider changing the setting that would allow you to manually turn on the REx engine whenever the battery pack charge level is <75%. This can be done using the BimmerCode smartphone app ($27 license fee) with a Vgate iCar 2 or 3 OBD-WiFi adapter (~$22 at Amazon).
BimmerCode allows one to make various modifications to personalize an i3, but these modifications aren't of the need to do immediately kind.