Financing construction projects - Enough equity?

We are still pondering whether we might have taken on too much. When building the house, we just don’t want to compromise on anything...

Plot: 1200 sqm, available, we got it from my parents
Planned costs for building a detached house, upscale standard with pool, sauna: €800,000
Equity: €150,000
Financing amount: approx. €650,000
Age: 28, 32
Children planned: No, definitely do not want any
Occupation: Teacher (both civil servants)
Net income: I €4350, she €3650. Total: approx. €8000
- ongoing expenses approx. €1500-2000 (private health insurance considered)
- savings rate (we do have a good pension but are reluctant to give this up): €1500
= surplus €4500-5000

Set repayment: €3500 over 15-20 years. This is significantly lower than our current savings rate (approx. €5500-6500), so easily manageable.

Is this realistic or better to save more equity, wait with building, or something like that?

So you definitely belong to the high earners. May I ask which pay grade you have? Because over 4000 net at the beginning of your 30s is already A15 (if I'm not mistaken), which surprises me a bit for a teacher.

Otherwise, you are worrying too much; with the repayment and the savings rate, you can definitely afford it. You seem to already live very frugally.
Maybe you can even forgo the equity and rather invest it elsewhere. Because your already existing plot of land also counts as equity for the financing of the house.

However, if a salary should ever fail (separation or other reasons), it will be very tight to manage the financing with only one income; you should also take this into account.

Net income: Me 4350€, Her 3650€. Total: approx. 8000€

Great income for two! You can really get started with that.

Planned costs for building a single-family house, upscale standard with pool, sauna: 800,000€

How big is the house supposed to be? Upscale standard - what exactly does that mean?
It's easy to reach the 800,000€, or even get close to a million if you have unrealistic expectations.

That completely depends on where you want to build. In MUC, that's not even enough for a standard terraced house.

I would start as soon as possible, inflation and the price increases will eat up any savings.

...
May I ask which pay grade you have? Because over 4000 net at the beginning of your 30s is already A15 (if I'm not mistaken), which surprises me a bit for a teacher.
...

I can't really imagine that. But that's not the topic here.

Yes, fits. If kids come, tight shorts. But you don't want any anyway.