This is a proof of a concept - and first I must admit, I didn´t reach the target - not even half way! But I learned a lot and will reuse some of the parts for a changed design.
And maybe this helps some else, thinking about creating a similar tool, too

(EDIT: In the meantime I created a camera slider, using the parts that were no longer needed here: The stepper, stepper driver, the arduino, the shield and a battery: https://www.thingiverse.com/thing:3042730 )

The primary idea was to create a kind of a programmable cablecam - with an arduino as a brain and a stepper-motor to move the thing.
There should be foldable arms for the rolls and and a simple system of two rods to carry a small camera-gimbal, that I use with my copter. So the basics were designed.

Then I tried several sketches to turn the motor forwards and backwards a different speed. Next I found code to read the pwm-signals from a receiver and finally I put thoose lines together and got a sketch, that lets me move the thing forwards and backwards by pushing the stick on the remote.

https://youtu.be/U8BPiDyFE8k
(The thing in the video is not leveled because there is no camera installed).

And that´s where I stuck. The motor is to weak although I tried higher voltage (12 V instead 2S-Lipo) and adjusted vref.
For a faster speed I need a bigger wheel which means a longer lever and less strengh …

Now I think about using a slow running brushless motor (about 600kv) and a car-esc. For a simple design like that, there will be no need for an arduino - but there will be no simple way to make it programmable either.
(With the stepper-motor there was the idea to count the steps while moving from A to B).