Maximum land costs compulsory auction

New construction without equity and thus no buffer is not a good idea even with the really good income. Existing properties would be the significantly better option, as the variables are much more manageable there. With a ~2000€ rate, quite a lot can currently be financed. The 500k are, in my opinion, calculated very conservatively; 100-150k more are definitely possible.

Inventory would be the much better option, the variables are much more manageable there.

Inventory + renovation is anything but manageable. There can also be nasty surprises lurking.

Existing property + renovation is anything but manageable. There can also be nasty surprises lurking.

Well, that is quite relative.
Sure, it sometimes happens that surprises are lurking.
However, they do not necessarily have to be fixed immediately.
If you have some experience with real estate and ideally let an expert inspect it, it is quite calculable.
Everything is there to begin with; with new construction, there are simply too many points that can be overlooked. From earthworks to outdoor facilities to insolvencies, etc.
It is simply not comparable, with existing properties you always have a roof over your head at first and can generally live in the house; with new construction, it can be a rocky road, as we have often witnessed here. For example, think of stories like that of the robber.

With an existing building, you always have a roof over your head first and can usually live in the house

It depends on the renovation. If it’s something bigger, you no longer want to live in it. Copper corrosion is one thing, electrical renovation another. These are no longer cosmetic repairs where you can manage without a children's room for two weeks.
And with existing buildings, you're at the mercy of the previous owner's or their predecessor's judgment. If they consider themselves McGyver, nasty surprises can also occur. Fully clad basement walls with a "small" damp spot, for example, are a hard-to-calculate risk for the buyer but would be avoidable with reasonable previous owners.

Inventory + renovation is anything but manageable. There can also be nasty surprises lurking.

As a tip, it was probably less about the forced auction of a house and more about buying existing property as such – with little equity as in this thread, this is generally preferable to purchasing land, no matter how.

For the purchase of existing properties:
We have found that you should even bring more equity to the table.
Here in the Düsseldorf area (and certainly in other dynamic markets) the sellers know exactly what’s going on: the market is practically swept clean and prices are really skyrocketing. Sellers calculate substantial premiums both on the official land value of the property and on their house value.

Unfortunately, banks don’t go along with this in that way. They want the difference between the bank’s valuation and the required purchase price to be secured by equity.
And 15k is unfortunately nothing at all.

In fact, there are no more bargains here. No seller is stupid. If there are, buyers outbid each other above the asking price.
Experienced exactly that...

@threadersteller
We end up with 148 sqm without a basement, without photovoltaics, with an air-to-water heat pump in absolutely standard equipment (already social housing here in the forum) at 265,000. But we have calculated 60,000 additional construction costs on top of that.
So we were and are extremely disciplined when it comes to the house costs. With additional construction costs, calculated with a good buffer.
300,000 is theoretically doable. But not with that equipment. And also too tight to sleep calmly. Not much can go wrong during construction.

It’s best to go to a seller and get an offer. That’s quick.
You will never get to the catalog price ;)