Cost of a single-family house with a full basement, 1.5 stories

Hello everyone!

We have now found a plot of land in our desired district in Berlin. However, we are tied to a developer and have now received an offer (actually the second one).

I would like to benefit from your experience and hear your opinion about our offer.

Floor plan roughly created
400 sqm plot in the second row
Subdivision still needs to be done
Connections are on the front plot
Fully biological sewage treatment plant is needed

1.5 stories with 115 sqm + 65 sqm basement (white tank)
Air-to-water heat pump
Central, controlled residential ventilation with heat recovery
Underfloor heating throughout the entire house
Chimney for a later fireplace
Cassette doors
Mullioned windows
Second wooden staircase to the basement (construction description specifies concrete)
Tiles in bathrooms, utility room and kitchen
Laminate in all other rooms
Master bathroom: tiled shower and tub
Guest bathroom: tiled shower
Sanitary fixtures from Villeroy & Boch, fittings from Grohe

Here is an overview of the costs of the offer:

Plot 120,000 euros
Brokerage fee 8,568 euros
Property transfer tax 7,200 euros
Notary 2,400 euros
Surveying 3,000 euros
House connections (water, electricity, telecom) 5,000 euros
Fully biological sewage treatment plant 12,000 euros

House price 264,264.50 euros

Total costs according to developer's offer approx. 422,955.50 euros

The only own contribution is wallpapering/painting the walls. Unfortunately, the developer does not allow more own contributions (unless you could take over an entire trade, e.g., roof construction).

The developer pays for the move and reimburses part of the kitchen for viewings during construction.

Now that is very much money and the house is really expensive. Or am I the only one who thinks so? Unfortunately, plots are more than scarce and I have been searching for a few years. For the first time, everything "fits." Whether we will get the money from the bank remains to be seen, but what do you think about the price overall?

Added to these costs are

Costs for subdivision
Building permit
Construction water and electricity
Mortgage registration
Land register entry
Structural engineer review
Insurances
Protection association
(additional earthworks?!)

... what do you think from experience, how much more should we calculate additionally? I feel a little overwhelmed by reading, planning, and organizing...

Thanks in advance to those who really read up to here :) and I look forward to your answers

Best regards, Kati