Stairwell edge insulation strip or not

Really not? It's the same - sand and cement - as the raw floor. Just a slightly different quality and unreinforced. I'm pretty sure I didn't misunderstand him. Both. So wood with metal rods.

Other quality, unreinforced, significantly thinner. But the staircase builder will know. With wood, it's also different than metal railings.

Not to be misunderstood. Where the railing is attached is, as said, composite screed. So only screed from the raw subfloor up to the floor covering. No insulation. Accordingly, there are 16 cm of screed there. The ceiling/the raw subfloor has a thickness of 20 cm if I am not mistaken. (Could also be 25.)