Sanitary shell inspection: What should we pay attention to?

Too late for PPS: Forgive me if I tend to believe institutes rather than manufacturers of heat pumps and industry associations in such matters. The BDEW also sees the gas heating system as future-proof because it can be operated with hydrogen or Power2Gas methane. But what else is the BDEW supposed to say? After all, it is THE lobby association for gas heating.

Nice that the thread is lively. :) Currently, we are still waiting for the current heat load calculation (35°C supply temperature) and the heat load calculation at my request (30°C supply temperature). I am relatively optimistic that we will come to a positive result. When I asked why the supply temperature was planned at 35°C and whether it could be lowered by a smaller pipe spacing, my wife said that we should rely on the expert. He replied that lowering the supply temperature can indeed be reasonable, but he would like to calculate it first. Therefore, I could imagine that 35°C is their go-to supply temperature because most builders don't care. The additional costs consist only of more material for the installation and a higher number of hours due to the closer loops, right? How much do you estimate this amount to be?

It is now September 13th and unfortunately there is neither a new heat load calculation nor have I received the old one.
As a reminder: During the shell construction inspection in mid-August, the managing director said that reducing the heat load calculation from 35°C to 30°C was not a big deal. However, the responsible employee at the company was on vacation for a week and then sick for another week. This week we asked again via our site manager. Now the plumber stated a processing time of 8 weeks because the heating/floor heating company has to do it.
Since the company is currently dealing with major renovations themselves, I assume they simply do not want to be dictated such an "extra task" by the builder. I expect to receive a defensive offer within two weeks.

Therefore, I would like to kindly ask again how expensive the additional installation was for you?

The additional costs are merely due to more material for the installation and a higher number of hours because of the tighter loops, right?
How high do you estimate this amount?

Our plumber plans the flow temperature of the heat pump at 35°C and installation distances always of 20 cm. I then asked for a cost calculation for around 30°C. (see attachment) I received this without further explanation. Before I start a conversation/discussion with him, I would like to have the following points clarified:

1) I understand that under the item "Length" the planned pipe length of the room is indicated. If several heating circuits are planned there, I have to multiply the "Length" by this factor. Is that correct?
2) I understand that more material (pipes, distributors, stapler clips) and more work incur costs. Did I forget anything?
3) If I understood 1) correctly, I come to a total length of 1,059.71 m and 17 heating circuits at 35°C and 1,929.2 m and 27 heating circuits at 28°C flow temperature. The difference is 869.49 m of pipe and 10 heating circuits more.
In which range should we currently be priced for this additional performance? Do construction costs skyrocket here or is this trade not affected by it?

The additional costs are expected to amount to 3,980 euros. I do not have individual items.

What do you think: Fair? Is the investment worthwhile over the lifetime of the heating system?

What do you think: fair?

The price increase is in my opinion fair. For DIYers online, the additional effort for the material is already well over €1,000. No "brand material" or normal wholesale prices but the cheapest online prices. Plus almost double the installation time. If it fits into the budget, then do it. In my opinion, it has many advantages and only one disadvantage. Advantages: - more comfortable floor because it is not as warm (yes, some women complain that the floor is no longer so "nice" and warm...) - energy savings - less power required from the heat pump = gentler on the materials - future-oriented, positive when reselling - reduces the CO2 footprint of your house Disadvantages: - costs money