Maximum and reasonable credit amount

General Information About You:

[*]Who are you? 36(m) and 33(f) married
[*]Are there children? Our first child is due in November 2025
[*]Are more children planned? In principle, another child is desired in the near future
[*]What do you do professionally? He: Insurance industry / She: Civil servant
[*]How many hours do you work? Both full-time

Income and Asset Situation:

[*]What income do you have (gross/net)? He: 3,500 net / She: 3,880 net (private health insurance already deducted)
[*]How much equity do you have? 250k (of which 155k ETF and 95k daily allowance)
[*]How much equity do you want to invest in the house project? 250k
[*]Additional income: We own a paid-off property. It is rented to the district. The tenancy ends in July 2027. Monthly income after all costs is about 3,000€ net. A continuation of the tenancy is generally possible but depends on many factors and is therefore not guaranteed. If the tenancy ends, we would most likely sell the property.
[*]Value of the property: approximately 250-300k
[*]Buffer account for property: 20k

Desired House:

If we were to fulfill almost all of our wishes, the house would probably cost (depending on the plot) between 600-650k€.

Expense Situation:

I will keep the expense side brief, as it is not the focus.

Together our expenses amount to 3,700 euros. Rent costs are 950€ cold and about 1,250€ warm.

Motivation of the Post/Question:

We live in the Rhine-Main area. The standard land value at the preferred place of residence is about 500€. However, when plots come on the market, location-dependent prices of up to 900€/sqm are paid (often in auction procedures).
Now I just want to find out what you think banks would consider a maximum financing amount possible for us.
What amount would you consider "healthy" under the given conditions?
Feel free to also give input on whether you would participate in these auction procedures.

If any information is missing to answer the questions, just let me know briefly.

Without further rents and the premise that you both work full-time, up to 750k is feasible depending on the interest rate. From a bank's perspective. I would personally consider around 600k comfortably affordable.

The premise of working full-time is no longer "fully feasible" due to the birth of the first child in November and the planned second child. I find the €3000 income for a €300k property interesting. How does something like that come about?

This is a special rental model (hence the fixed term) with significantly above-average wear and tear.

This is a special rental model (hence also the temporal limitation) with significantly above-average wear and tear.

We all know what that means, right? Surprisingly, though, the rental costs are low.

The premise of working full-time is no longer "fully sustainable" due to the birth of the first child in November and the planned second child.

Depending on life planning, this is a transitional period that is quite manageable. However, the OP has not written anything about that.