Own property right from the start? A beginner needs straight talk...

To come back to the question of the OP once again:

You might want to take a closer look at/explain your expense side. It’s written a bit oddly. Maybe I understood it correctly:

Fixed costs: 2,400 euros
Monthly savings rate: 1,400 euros
Plus rent (warm): 830 euros
(Living-)costs: 570 - 770 euros

Does your wife work? Does she have an income or have you left her out completely since the planned child is coming soon? Then there might possibly be an additional buffer (income or parental allowance + later income).

I am now assuming 1,400 euros + 500 euros cold rent: 1,900 euros per month for the loan installment
1,900 euros x 12 months : 4.5% (assumed annuity) = approx. 500,000 euros potential loan <--- should fit

How are the 80,000 determined?
Are the current 1,400 euros going completely into the designated investment?

Depending on where the 80,000 euros are invested, you can also use this asset as collateral (assignment of an insurance policy, pledge of a depot, etc.)
Do you have the money in a condominium: mortgage on the condo
Is the money in a savings contract that is not yet eligible for allocation, you can play with the loan terms:
70,000 euros over X years (allocation maturity) + 100,000 euros KfW + remaining loan (or the allocation maturity is only reached when the KfW is about to mature - then repayment with the savings contract).

Judging by your nickname - you are 44 years old: keep in mind with your loan that you should be done in about 20 years so that you go into retirement "debt-free."

Oh guys... why are you getting so worked up again? Just as a reminder... I had written: "Neither is 3.2k earning very well nor is a 26-year fixed term sensible."

It doesn't say that "3.2k is bad or normal," it says it's not VERY GOOD. Always in the context of a builder who wants to build a house in 2016. Does anyone seriously want to contradict me on that?! I would rather call 5k+ from the original poster very good.

And why 26 years are hardly sensible has already been explained here several times in other threads. Of course, it depends on the individual case. If the whole financing is tight, then a full repayment probably makes sense... but even that is not the rule. Currently, only 15... max. 20 years really make sense. I would describe 15 years as almost perfect.

. Of course, it depends on the individual case.

And you could have saved the rest of the text because it applies to nobody and everybody.

And you could have saved the rest of the text because it applies to no one & everyone.

No, I actually forgot something -> If it's tight, you better not build a house

Steffen's wisdom - in the text before, he also said that in a tight financing a full repayment makes sense.

and then came "...but that is not the rule either"