Construction costs are currently skyrocketing

With the 24 KS stones maybe yes, but actually the WDVS should prevent any cold from reaching the stone. ;-) In my opinion, this is merely a liability waiver by the plumber. Due to the chiseling measure of 2.50m high in KS, I wanted to accommodate him and take away the hassle of those 50cm. :D Plaster? Yes yes according to the offer but I prefer to save the €35/hour since I’m just putting tiles over it (see picture 2) ;)

Well, probably no frost damage, but with the typical 36.5 cm plan stone wall and 40mm wastewater/drinking water pipe + insulation, you chisel away almost a fifth to a sixth of your insulation. That could already create a thermal bridge, especially behind the kitchen cabinet where warm vapors often reach. So potentially a risk of mold after a few years if you don’t check.

This electricity price story depends on the region, between North and South there can easily be a difference of 10-15 cents.

I have looked at it again in more detail and believe that with N-Ergie it could be because 1. they now only serve regional households and businesses (which should save them quite a bit on grid charges), and 2. they produce a lot of electricity themselves. So I just checked again: heat pump electricity I have even in the off-peak 15.xx cents and in the peak 18.xx cents and for domestic electricity 25.xx cents. The basic fee is about 10.xx € per month. The next cheapest tariff on the local portals is more than twice as expensive. 52.xx cents and 13.xx € per month. Apparently N-Ergie is also very fair and does not exploit the general situation. We seem to be really lucky in our region.

Is there really a risk of frost damage in the water pipes with the thick walls today?

Frost damage probably not, but if you plan a monolithic wall construction, that spot is a weakening of the thermal envelope. The energy consultant then has to calculate it, if necessary a thin insulation will be applied from the inside, etc., so ultimately effort (=money) but doable.

Yes, we build monolithically with 42.5 cm Ytong and also have the sink on the exterior wall. I'm curious to see what the plumber will do when he returns from vacation and starts working at my place. The refrigerator is on the other side on the interior wall, so in that regard it's unproblematic.

Frost damage probably not, but if you are planning a monolithic wall construction, the spot is a weakening of the thermal envelope. The energy consultant can then calculate this, if necessary a thin insulation is applied from the inside, etc., so ultimately effort (=money) but doable.

According to your logic, you would then have to struggle with mold at every window frame and opening ;) A 7-chamber window profile with a U-value of 0.8 is definitely comparable to a wall cutout of over 30 cm with a monolithic wall thickness of 42.5 cm. Ventilation pipes, drainage, chimney for fireplace, outdoor sockets .... there are countless thermal bridges. But that is normal in a house, even with kfw40. Usually something like this is fixed anyway with "foam sealant", no one sees it afterward. Foam sealant is a good insulator