keepee: Thanks a lot for your reply, this one sounds quite promising and I will give it a shot.
In the meantime I kept on experimenting some more and it looks like my impulses are working out so far...
Framerate independent movement activated AND dt on my impulse gives me satisfying results... must have overlooked this earlier because rotation still won't work as it should:
I'm rotating my object by applying torque
without dt rotation on lower framerates is much too slow and with dt rotation on lower framerates is much too fast.
When measuring the angular velocity of my Sprite using "Sprite.Physics.AngularVelocity" WITHOUT dt I get the exact same values on all framerates, while still on lower framerates my sprite is rotating much much slower than on 60FPS.
This seems odd, because the manual says AngularVelocity outputs "The current angular velocity (rate of rotation) of the physics object, in degrees per second." and not degrees per tick or something.
So I'm still struggling^^