Simple transistor circuit not working
The motor gets basically no current and the voltage at the motor is
not the expected 12V but 1.2V?

Your NPN transistor is acting as an emitter follower and, if the 100 kΩ resistor were more like 100 Ω then you might see 4 volts on the motor when it is activated. This is what happens when you use an emitter follower - the emitter follows the base voltage (with a slight voltage reduction). However, when using a 100 kΩ resistor, the current into the base multiplied by the transistors β (circa 100) doesn't produce much emitter current and it will appear that the motor is not powered.
If I were you I'd look into using a P channel common source MOSFET to switch the motor on and off. Or, use an N channel common source switching the negative supply to the motor. Get this bit working before adding any sophistication.