Interesting house construction offer? Experiences?

Hello everyone,
I need your help. We have some very concrete offers on the table for the construction of a detached single-family house on a reserved plot in the Recklinghausen district from Fingerhaus, ProHaus, Fingerhut-Haus and, for comparison, Town & Country and roughly Heinz von Heiden.
We have ruled out the prefabricated house manufacturers mentioned above due to too low a budget and lack of price transparency. Here, the estimated additional construction costs ranged between €13,000 and €25,000, which is significantly less than the (realistic) approx. €40,000 listed below.
After a very good consultation, I would be interested in your opinion on the following list:

Total costs of house construction (living area approx. 145m²)

[*]Colored roof soffit

[*]Underfloor heating throughout the house

[*]Attic lighting including switch

[*]Electric car connection

[*]LAN package: Patch panel Cat7, 6 connection sockets

[*]Side panel at the front door

[*]Electric shutters throughout the house

[*]Windows and front door in special colors

[*]Additional window 100x137.5cm

[*]Walk-in shower

[*]Additional walk-in shower on the ground floor

[*]Bathroom radiator as towel holder

[*]Tile package: tiled kitchen, tiled splashback on the wall, hallway/entrance ground floor, utility room, tiled including €25/m² tiles

[*]Changes to ground plans ground floor, upper floor

[*]Soil survey, official procedures, trade coordination, etc.

Total price including all listed extras: €223,550
Plot costs 585m² (including development etc.): €117,000
Additional construction costs

[*]Real estate transfer tax 6.5% €7,605

[*]Additional costs for plot acquisition (e.g., division, mortgage agreement) €3,500

[*]Notary 2.0% €2,340

[*]House connections (electricity, water, gas, telephone) approx. €4,800

[*]Multi-utility house entry provider €1,250

[*]Leakage test for sewer according to DIN €450

[*]Wastewater: sewer connection, if necessary inspection shafts €6,000

[*]If necessary, infiltration system for rainwater (if required) €2,500

[*]Building permit approx. €1,000

[*]Additional foundation investment (additional foundation, possibly removal of excavated soil, possibly foundation elevation, construction fence, possibly drainage, possibly geotextile) approx. €6,000

[*]Additional foundation investment €3,000

[*]Surveying fees (site plan, staking out) approx. €2,000

[*]Cadastral final surveying approx. €950

[*]Provision of construction power and construction water WC (flat rate) €1,750

Total additional construction costs €43,145

Special expenses

[*]Outdoor facilities (with own services) driveway, front garden, terrace €15,000

[*]Concrete prefab garage including foundations 3x9m €11,000

[*]Shower enclosure, attic flooring €2,000

Total special expenses €28,000
Other options: instead of gas heating with solar thermal, an air-water heat pump heating system: €5,000
Ventilation system with cooling function: €5,000, but no details are known yet.

Overall, a plan for €411,695, whereby we can save on outdoor facilities through own work.
From my point of view, a reasonable financing offer is available; I would be interested in your opinion on this offer.
Our fixed budget is €420,000; a little more is of course still possible. Furniture, kitchen, wall and floor coverings still need to be added and will be installed as own work.

I am looking forward to your opinion!

Fits so far, but you need to plan 50,000 as a buffer. The house is very tightly budgeted. 25 euro tiles are not a great quality.

Thank you for your assessment, thank you for taking the time.. A €50,000 buffer is quite a lot. Unfortunately, we will not be able to raise that. However, I also wonder (naively) what this might be necessary for. As a "hard" reserve, we still have €10,000 that we could access. But that's it... However: if we had more, we would probably also bring it in as equity...

You have, in case something gets out of hand during earthworks, buffers in the construction execution: white instead of colored windows: saves about 2000 and is qualitatively identical. E-car connection can be omitted. Roof soffit can be white. Roller shutters are not necessary. In this respect: it can work to stay within the budget. Set a dogma, swear it to yourselves, seal it with your blood: if somewhere 10.00 euros more, then always 10.00 euros less elsewhere.

if somewhere 10.00 euros more, then always 10.00 less somewhere else.

I think so too. Of course, it is clear that we are calculating very tightly. We might possibly also expand our budget a bit. It is doable, but the monthly burden then becomes too high for me. At least it feels that way ^^. The financing conditions are: Financing amount: €395,000 Interest 2.25% Fixed interest period 15 years Repayment 2% Monthly rate: approx. €1450 Against this are €5400 net income, 2 adults, 2 children

I wouldn’t spend more either. After all, you don’t want to slave away for the house your whole life or always fear that if something goes wrong, it will lead to foreclosure. Less is more.