For strange reasons, WH does not offer pure aluminum windows, but only Kunst, wood, and H-A.
The aluminum shell is useless, so depending on the desired surface, just take PVC or wood.
Regarding the gravel screed, I actually asked for additional school protection when I realized that in a FH (based on a visit to the building center) you can hear someone walking much more distinctly on the first floor than in a solid construction. To mitigate this, the lady from WH suggested the gravel screed for an additional cost of 3k, but I have no idea if it really makes a difference. I couldn’t find much about it on the internet.
You found me on the internet - and my knowledge is enough to tell you that except for at most a placebo effect, there is nothing to gain from it. I would even advise against it unless they have thousands of experiences with it; otherwise, you’re almost certainly creating grounds for complaints. My stone mantra also applies to floors.