Height of power outlet for fridge-freezer combo?

Yes, just like in your pictures was the original idea.

Hm, I would probably choose the safety variant and set it high enough. It will be a 1/4 spiral staircase.

Attached is also the position of the 1st lamp again. 2.4m from the raw floor level. If I subtract the floor structure and the possible height of the staircase at the position of maybe 50cm, you would even have about 1.7m distance between step and wall lamp there.

Yes, just like in your pictures was the original idea.

And why not implement that?

Hmm, I would probably choose the safe option and set it high enough. It will be a 1/4 spiral staircase. Attached is also the position of the 1st lamp. 2.4m from the raw floor. If I subtract the floor structure and the possible height of the staircase at the position of maybe 50cm, you would even have about 1.7m distance step - wall lamp there.

Up to the X a conduit and you have all options open. Later you only have to drill a hole in the conduit once, pull the cable through and wire it accordingly in the distribution box. As mentioned about 30-45min effort. But without a conduit it won't work without an exact staircase plan and even with a staircase plan it is more complicated to measure everything than simply drilling a hole afterwards. In this photo it might still be possible to lay the cable, but at the latest on the "longer" side you won't hit the exact slope of the staircase.