Financing purchase project single-family house 580TE before upcoming parental leave

And do you really want to tie yourself to a year of construction where everything can break that you haven't renovated yourself, since you don't know how thorough the previous renovation was?

So, for a volume of 700k€, investing in an almost 70-year-old house, everything must already be scoured out within a 30km radius.

Well, according to the market situation, the property is "fairly" valued. It's all relative. I would also like to buy a single-family house for 400k€, but that won't work. I want to stay within a maximum radius of 5km. Everything else is currently out of the question.

max. 5km bleiben

I understand. That’s tough. Fortunately, I talked my wife out of something like that, otherwise we would still be stuck in a rental apartment within a similar radius. Means 760k€ (580 x1.1 +120) total volume -120k€ equity = 640k€. The bank probably values the property significantly lower than 580k€. Therefore, I believe that not only the income will be a challenge, right?

And do you really want to tie yourself to a year of construction where everything can break that you haven’t renovated yourself, since you don’t know how thorough the previous renovation was?

I see it similarly. For €120,000, the house certainly won't reach new build standards. 170m² at €1000/m2 core renovation costs already points in that direction. But putting that aside: "flooring, kitchen, doors, electrics / water pipes." What about the heating system? Do you still want to stay with gas, or are you switching to a heat pump + underfloor heating? And if so, can you insulate the house accordingly on the exterior walls? Should rooms be enlarged/combined? Should larger windows be installed? How old are the windows? What else needs to be done on the outside?

Well, according to the market situation, the property is rated as "fair". It's all relative, of course. I would also like to buy a single-family house for 400K, but that won't happen. I want to stay within a radius of max. 5 km. Everything else is currently out of the question.

Where are new construction projects located in your area? And how high is the land value proportion of the whole? It must be at least 400€/m² or more...

Preliminary:
Personally, the construction year wouldn’t deter me. However, one must be aware that it will always remain an older property. Renovation or not.
Some buy and renovate an old thatched cottage and are happy with it because they recycle and love that the house tells stories with creaks.
You have to be clear that while the foundation masonry can be very solid, it can also start to grumble over time.
I always say: an old house is a hobby.

Must: bathrooms, floors, kitchen, doors, electrical / water pipes (do you have to forcefully renew the ones from the year built?)

For example, I would only paint the doors for the charm and not replace them. Electrical systems should be redone because of the new standards. I don’t know about the water pipes. After all, only water runs through them.
Bathrooms: old bathrooms often have the tiles that are fashionable again now… but I assume a renovation from the 80s, and you definitely don’t want that anymore.

Should / Can: windows (wooden frames), insulation (the house from 1955), attic, basement ceiling, paint exterior facade

You can renew the glass in the windows. …
I would have the insulation done; it was quite minimal back then.

Insulate / insulate attic, insulate basement ceiling

That probably has to be done according to today’s EEF?!
That could all turn into a bottomless pit. Then the desire for new roofing comes up because a dormer is needed, and so on.
Many would probably rather tear down the house and build new there.
Question: what do you want to achieve? A quasi-new build?
Do you have any photos? How come an architect is already involved? Have you been considering the property for a longer time?

So, I have to be honest, this is really borderline, even with your two salaries. If this were a new building from the developer with a price guarantee, I might just say: Yes, it's somehow doable. But here you have a significant risk, the risk of the "hidden." You only see that once you tear the place open. There is probably little room for additional financing in an emergency. In the end, only the family remains; would there still be something to gain if push comes to shove?