@breimann , all of that will take a few posts to explain. Bear with me.
The door mechanism took a lot of trial and error. My biggest advise is to estimate the torque needed to open the door before ordering any components.
Due to lack of a dynamometer, here is how I tackled the problem :
Attach an elastic band to the door at some position where you know the distance to the hinges (15cm in my case)
Pulls the elastic band towards you in a right angle to the door until the door starts to move. Measure or estimate how much the elastic band is stretched (in my case, I measured +/-30cm). Be careful the door doesn't smach into your face
Disconnect the elastic band from the door and suspend some adjustable weight to it until it is stretched the same amount as before. I used a small bottle, an iron wire and changed the amount of water in the bottle.
Measure the weight
The torque is distance (to the hinges) x the weight, in my case 15cm x 0.285kg = 4.275 kg.cm
I selected a Modelcraft RB350600-0A101R Transmissiemotor 12 V 1:600 (25€ at Conrad).
According to the datasheet, at 3.44kg.cm (closest in the list), the motor should run at 9,46 rpm and consume 0,14A (12V).
In reality, the motor takes about 3,5s to make half a turn, which amounts to 8,6 rpm and pulls between 150 and 200mA with a startup current of +/- 350mA. Pretty close to what the data sheet says !
For the actuation of the motor, I use two relays of a Seeeduino relay shield of which I connected the NO to 0V, the NC to 12V and each motor wire to one of the COM. The resulting behavior is
R1 open, R2 open ==> motor stops
R1 closed, R2 open ==> motor turns CW
R1 open, R2 closed ==> motor turns CCW
R1 closed, R2 closed==> motor stops
Some more advise,
Don't try to open the door with a stepper motor. i tried it and I got bad oscillations.
A servo motor could also work, but you'll have to find one that can deliver the torque.