Purchase opportunity single-family house from the 80s - risk?!

I don't exactly know "where" you are right now. In NRW, for example, there is a refund on part of the property transfer tax for residential property purchased this year. The date of the notary appointment is relevant there. But that is specific to NRW.

Unfortunately, I haven't found anything similar for Lower Saxony. Does anyone possibly know?

Something about the process: We have calculated approximately 100K for modernization, with about 1/4 of the work to be done by ourselves: children's room, study, and bedroom floors and walls renewed, insulating the attic floor. In addition, the bathrooms will be partially renovated by "acquaintances." Does the bank definitely want a statement and invoices for the 100K modernization in advance and after the renovation? How did you pay your acquaintances? We are quite new to the whole area and still learning ;-) ….

We have spent about €90k. New electrical system, network, terrace roof with glass (convertible roof), bathroom and guest WC renewed, partly new floors or parquet sanded and sealed, partly new radiators, new gas heating, new windows, electric shutters, a lot of drywall work, insulation added in the attic. We did the wall coverings and preparatory work ourselves, such as sanding and priming the walls. The kitchen remained as is. Next year, the gable wall and dormer will be insulated, and the remaining radiators will be replaced. The new gas boiler became necessary because the old one was about to fail and the house is not yet ready for a heat pump (not to mention the prices). In my opinion, the €100k budget is well calculated (the most expensive part is labor), especially since new (and sensible) ideas keep coming up. "Since you’re already working on it and don’t live in it yet…" ;)

Unfortunately, I have not found anything similar for Lower Saxony. Does anyone possibly know?

It was/is only in NRW, as a state tax. Here in NRW we have 6.5%, which is definitely quite high. The discount for owner-occupiers is 2%, but it is supposed to be only a transitional solution until a reform. Lower Saxony is relatively "cheap" with 5%, I don't know to what extent there will be a reform there.

We spent about 90,000 euros. New electrical system, network, terrace roofing with glass (convertible roof), new bathroom and guest toilet, partially new floors or sanding and sealing of parquet, partially new radiators, new gas heating, new windows, electric shutters, lots of drywall, attic insulation added. We did the wall coverings and preparatory work such as sanding and priming the walls ourselves. The kitchen stayed as it was. Next year the gable wall and dormer will be insulated and the remaining radiators replaced. The new gas boiler became necessary because the old one was on its last legs and the house is not yet ready for a heat pump (not to mention the prices). The 100,000 euros are, in my opinion, well calculated (the most expensive thing is labor), especially since new (and sensible) ideas are still coming. “If you’re already at it and not living in yet…” ;)

How did you handle the proof for the bank? Can I also claim own work or wages for acquaintances/friends? How is that proven?

The bank only wanted an approximate breakdown of the costs. These were not financed by us but borne from the assets, so I cannot give a reasonable answer to that, sorry.