Financing a single-family house with land subdivision - risk or opportunity?

Hello everyone
My partner and I are closer to buying a house than ever before. However, the financing still gives (especially me) a bit of a stomach ache and I am unsure whether we are taking on too much here.
What is your opinion regarding the project below?
Due to a necessary subdivision of the plot, there are certainly further risks for us but possibly also opportunities.
In summary, it can perhaps be put like this:
Single-family house in prefabricated construction on a small but expensive hillside plot in the Stuttgart area.

General information about you:

[*]Who are you? Partner + me
[*]How old are you? Both 30 years old
[*]Do you have children? No
[*]Are children planned? Yes, 2-3
[*]What do you do for a living? Development engineer, controller
[*]Are you employed? Both employed
[*]How many hours do you work? Both 40h/week

Income and asset situation:

[*]What income do you have (gross/net)? approx. 7,800€ net
[*]How much child benefit do you receive? 0€
[*]Other transfer payments such as parental allowance, sick pay, etc...? 0€
[*]How much equity do you have? approx. 275k€
[*]How much equity do you want to invest in the house project? Unclear... due to buffer and plot subdivision and corresponding financing, possibly 200k€

Expense situation:

Housing costs:

[*]current cold rent, 1100€
[*]current warm rent 1350€
[*]household ancillary costs including food and other bills (electricity, internet, waste): 450€

Mobility costs:

[*]Leasing 356€
[*]Insurance 53€
[*]Taxes 19€
[*]Fuel 33€
[*]Repairs 135€
[*]Second car
[*]Insurance 41€
[*]Taxes 13€
[*]Fuel 25€
[*]Repairs 25€

Insurance costs + retirement provision + disability insurance + etc., jointly

[*]Together including all: 1200€
[*]House savings: 600€

Living expenses, jointly:

[*]All ancillary costs, shopping, hobbies, etc.: 1000€ (estimated)

Income and expense totals:

[*]Total income: 7800
[*]Total expenses: 5600
[*]Balance: 2200
[*]of which sum cold rent and dispensable savings (e.g. savings rate for house): Rent 1200 (incl. parking space), 300€ BSPV, 300€ savings rate

General information about the property:

[*]How large is the plot? 650m2 before subdivision, afterwards 335m2, 315m2
[*]How high is the plot value? 550€/sqm
[*]New build, old building (year built), type of house? New build, single-family house 1+basement, prefab house Bien-Zenker including basement turnkey
[*]Garages? Double garage
[*]How big is the house? (living space / usable space) 180sqm
[*]A granny flat in the basement is planned for commuters.

Construction or purchase costs:

[*]Total costs 945,000€ (incl. assumptions)
[*]Assumptions:
[*]Plot costs after subdivision including ancillary costs 374,000€ (before subdivision 660,000€ without ancillary costs)
[*]Buffer (sample selection, furniture, kitchen, general): 50,000€
[*]Additional construction costs: 45,000€
[*]Cost of house (currently estimated): 520,000€ (incl. basement, solar, turnkey)

Cost summary:

[*]Total costs: 945,000
[*]Deductible equity 20,000
[*]Financing amount 745,000

What is your question? The story with the [Grundstück] is completely incomprehensible. On which [Grundstück] are you building? 315 or 335 sqm? The house is too expensive.

I am just wondering how one is supposed to fit a double garage and a 180 sqm house on one of the two future plots. That leaves no garden at all. Don’t [Grenzabstände] have to be observed?

Are you buying a plot of land and want to divide it and sell one half again?
Why an accessory apartment? It costs a lot of money upfront, and it's questionable whether you'll ever get that money back.

Hello,

thank you very much for the answers.
The concrete question is actually only whether the project is too optimistic or realistically feasible.
Maybe a little more detailed background.
We have an offer to buy a 650 sqm plot. However, we would have to divide the plot, as otherwise the costs would be too high. The plot would (according to the current plan) be divided in the middle, resulting in (due to the trapezoidal shape) a plot of about 335 sqm and a plot of about 315 sqm. The smaller one is to be resold.

On which plot are you building? 315 or 335 sqm?

We want to build on the 335 sqm part.

The house is too expensive.

I made a mistake there. 520k€ include 50k€ incidental costs, I must have slipped in that line

Then there is no garden left.

So-so, there simply isn't much supply and current prices are just incredibly high It is a sloping plot and the 180 sqm are spread over 3 floors, whereby that is the pure floor area. It is partially supposed to be integrated and thus not occupy 6x6m. The house is currently only a proposal, we haven’t been to architects etc. yet.

Are you buying a plot and want to divide it and resell one half?

Yes, completely it is too expensive, selection in our region is very limited. 1000€/sqm is "normal"

Why a granny flat?

Higher subsidies and rental income, the space is simply there due to the three-story design

You are definitely among the top 5% of the highest-earning childless couples in Germany, have almost 300k in equity, and still have to do the math, crazy.

For your land costs, we could buy a new semi-detached house here 70km from FFM, including a similarly sized plot. Something to think about (or maybe better not)...

Conclusion: The prices are insane, but you can probably still afford it. The rate will surely be 2.5k+ though. I would recalculate that with parental leave or part-time work for the woman, she will hardly want to go back to full-time right away...