Affordable modular construction - is my calculation realistic?

Hello,
I have a request for all experienced home builders to check my calculation to see if my numbers are realistic.

For explanation:
There are only two of us left, we want to sell our house and build a small 100 sqm bungalow without a basement. Heating will be with infrared heating. A lot of own work is possible. To make the whole thing as cheap as possible, we have tentatively selected the Austrian modular building system [combi-box].
As a calculation basis, a 108 sqm floor plan from the [combi-box] website is used, I suppose I am not allowed to show the link?

The numbers for the "shell construction" come from [combi-box], for all the others I tried to estimate correctly, as mentioned, everything should be very budget-oriented and done with own work. According to [combi-box], the sanitary and electrical installation can be completed in about 30-50% less time.
So please mainly look at my estimated numbers. I hope, plus a buffer of about 15,000, to come to a total of 150 thousand without land.
I would appreciate your replies, thank you.

Numbers from [combi-box]:

Modules € 32,700.00
Windows € 3,740.00
Subfloor € 3,260.00 (less without screed)
Walls/Ceilings € 7,320.00
Facade € 2,910.00
Shed roof € 8,030.00
Earthworks € 8,030.00
Insulation € 2,670.00
Building application € 1,380.00
Transport costs 3 trucks € 5,400 (possibly 40% less)
Assembly costs € 1,200.00

Subtotal € 76,240.00
Value added tax € 14,485.00

TOTAL Shell construction € 90,725.00

Own estimates:

Connection fees water/sewer ~ € 2,500
Public development ~ € 3,500
Connection fees electricity ~ € 1,500
Front door ~ € 2,500
Window sills inside ~ € 1,000
Window sills outside ~ € 1,000
Window shading ~ € 1,500

Electrical installations ~ € 4,500
Sanitary installations ~ € 2,500
Infrared heating ~ € 5,000
Outdoor chimney ~ € 1,500

Tiles (bathroom WC) ~ € 1,000
Bathroom and WC fittings ~ € 2,500
Floor coverings final ~ € 4,000
Kitchen ~ € 5,000
Lighting ~ € 500
Other fixtures ~ € 1,000
Overall static (only necessary in Germany) ~ € 500
Outdoor facilities ~ € 5,000

TOTAL estimated numbers € 45,500

TOTAL WITHOUT LAND € 136,225

Without knowing your property, nothing can really be said about the outdoor facilities and earthworks yet. Should the foundations also be included in the 3200 € subsoil? Many small items are missing from your own services: construction toilet / construction electricity / construction fence / etc. So already plan around 5,000 € for small expenses. Bathroom and WC for 2.5 k € including materials? That won't work. Without knowing the provider, it is difficult to say that it will work out. Why the installation should be so much cheaper with a container is not clear to me.

Hello, thanks first of all.
So, the plot does not exist yet, so we can only calculate a lump sum for now.

Subsoil and earthworks are composed according to the provider as follows (lower limit):

Earthworks in the size of the construction project (excluding access road, forecourt, etc.)
Set up construction site:
750.00
Excavation and disposal:
1,850.00
Frost cushion material:
2,310.00
Point foundations:
1,120.00
Miscellaneous: 2,000.00
Earthworks (excluding connection fees) total:€8,030.00

[B]Subsoil[/B]
Subsoil with flowing screed:
Material costs subsoil (25mm OSB boards, vapor barrier, small materials):
880.00
Labor costs laying subsoil:
760.00
Costs flowing screed including laying and sanding:
1,620.00
Optional, total price subsoil with flowing screed: € 3,260.00
The subsoil is laid with OSB boards (25mm) on our floor construction after completion of electrical and sanitary work. Final coverings are not considered due to the variety.

It is clear that quite a bit is still missing, for that I have added another lump sum of 15,000.

Bathroom/WC: is calculated ambitiously, I know, but tiles and floor are already extra, and with simple white hardware store goods it should be doable.

Why the modular construction is cheaper is currently only told to me by the provider's website. It is a pity that I am not allowed to name it here because no one would know what is being talked about; I really have nothing to do with them. Anyone interested can send me a private message, or they can enter "Lustenau combi" into the search engine, then they should find it (I hope I am allowed to say this?)
I have not yet obtained counteroffers from wood or stone builders.

Best regards