- I want even to go futher then sleep mode, and use a key of the keypad to power up the whole circuit. The arduino should power off the itself and the whole circuit after unlocking the door. Is this feasable?
Yes. Circuit can be powered off even, and awakened with a button press.
All the devices can be powered off when in the locked position. Have a spring loaded door that is pushed open when the lock retracts, and the door have a tongue that can slide over the lock to push close (poor description, go look at any house door, it can close without turning the knob, yes?)
As to which takes more power to pull the lock arm out of the way, you'll have to experiment.
How far does it have to move? How durable does it need to be? How much does it have to resist being broken into? etc.