ThaReaper:
I considered a DC motor, but i wanted to keep things simple. a Stepper could lower and raise the door an exact number of steps, and that way i shouldnt have to use endstops if i calibrate it well.
How can you know at which position the stepper is upon startup? Or what if the stepper misses some steps occasionally?
You may consider using a servo, they're much more power efficient than steppers, and have absolute positioning. It's quite straightforward to slow down the movement using software, to the speed you want (the inertia of the door also slows it down, but unlike a stepper you always know where you are as there are no steps to be missed).
A counterweight (or spring) on the door is also a good idea, then your motor doesn't have to work so hard to open/close the door. That's another serious option for power saving, even though the movement is only 2x 10 seconds or so a day, especially when done with a stepper it may take as much power as the Arduino uses the rest of the day.