Home purchase financing with little equity?

House is not smaller than the apartment. It has a basement and also an attic. We previously lived in a house for rent. There we only had slightly higher additional costs than now

PS. Kitchen is available. The pipes in the house are actually also fine, but if everything is not redone before moving in, then never... Because once you live in it and want to renovate all the pipes at some point, it will be fun.

Uhh. €20,000 and a complete renovation... you alone should have the €20,000 as a buffer for all the things that will become apparent to you during the renovation of a 1950s house that you haven’t considered. The plan is completely unrealistic.

And you still haven't answered who estimated that. And who said the substance is good.

Did an appraiser do that or did you find out by knocking on the wall three times?

As said - the term major renovation is perhaps a bit poorly chosen ... but I will take another close look at material prices.

But back to the topic of financing .... what options are there to achieve the most affordable installment with high repayment?

Loan
KFW
Riester
Building savings
Private loan (expensive)

Oh yes ... local real estate prices are exorbitantly high .. a move-in-ready house that is somewhat modern starts here at around 350 and up ... and the old wallpaper is still stuck on the wall .... there are absolute junk properties we have looked at for 280k euros, so the mentioned property is really a "bargain" - moving to the middle of nowhere is not an option for us.

Don't fool yourself into thinking it's a bargain (unless you buy from relatives at a discounted price). If no one wants to pay more than you, then that's just the market price, but definitely not a bargain.

You seem to want to justify/argue it all quite nicely for yourself. Everyone here is telling you that €20,000 is not enough, yet you still believe it. It will not even come close to being enough, and if you base your already tight financing on that, it could possibly break your back. Alternatively, it will be a 15-year-long construction site, ...

By the way: As cheap a rate as possible with as high repayment as possible ... that excludes each other. Never repay less than 2% and you'll have to take whatever interest rates the banks offer you anyway. You can easily calculate what your rate will be. With an annuity of 4% and a €300,000 loan, you have your €1,000 monthly rate. But keep in mind: With such an old house without a proper complete renovation, you have enormously high maintenance costs and also additional costs due to heating! The maintenance costs alone certainly amount to several hundred € per month on top.