For those receiving a new phone or watch on Friday, you may want to wait until you receive your new device if you want to restore from a backup. You won't be able to restore a backup from iOS 12.1 or watchOS 5.1 to a device on iOS 12 or watchOS 5. If you update your current device now, you'll have to set up the new devices on Friday as a new device, install the beta profiles, update, reset the device, and then restore from a backup.
This... I've done that before, and it was not fun.