First, the easy one: the back-up warning is normal. It's purpose is to warn those outside the car, where the sound is louder.
As far as the transition from engine to battery and vice versa is concerned, what you are describing is NOT normal. At normal driving speed, there is absolutely no physical indication that the engine has cut off or come back on. When the car is at rest, or just moving a couple of mph(or in your case, kph), there is the slightest "shudder" at the transition, but it does not impact the drivability of the car. If your dealer still insists that your car is normal, try another dealer, if possible, or if that's not possible, you need to contact Infiniti directly.
As far as the transition from engine to battery and vice versa is concerned, what you are describing is NOT normal. At normal driving speed, there is absolutely no physical indication that the engine has cut off or come back on. When the car is at rest, or just moving a couple of mph(or in your case, kph), there is the slightest "shudder" at the transition, but it does not impact the drivability of the car. If your dealer still insists that your car is normal, try another dealer, if possible, or if that's not possible, you need to contact Infiniti directly.