Thanks for you help!
I think I'll just test it out.
(the motor is on the way from China)
But some questions:
The motor doesn't stand still for a 'long' time or? Are 0.269250 seconds per step such a long time for holding the motor to lose steps?
About the current I maybe have to say something about my plans on powering it:
The Arduino will be powered directly from my power bank. From there I connected an DC/DC step up (5 to 12V) for the motor.
I connected an 7.5 degree motor for testing and the motor was turning. So I hope the Nema will work also 
I'll let you know when I finished the mount for testing!