Build a circuit that includes the micro-controller and Bluetooth to do the image processing and connection to the user phone.
Develop the code to do the facial recognition (It may be necessary to buy licenses for different library so that it is not required to build our own image processing library.) and the phone recognition.
Build the casing for the micro-controller circuit.
Build the motor locking and unlocking mechanism.
Finish up the project by making sure it is as secure as possible.