House construction 2022 how to approach best?

We would even go more northerly. But 300€ per sqm is the limit.. It should be around 600sqm +/-.
We are currently looking at everything in the area of Wuppertal, Düsseldorf & Cologne. There are several cities or municipalities there.
I check both Immoscout and the websites of the cities almost daily.
Maybe someone has a tip..

Regarding the house costs, thanks to you I have already got some good reference points.
Then we would probably come to about 550,000-600,000€ without furniture and kitchen for 180sqm without land. The land would be added separately.

Northward towards Düsseldorf, it becomes more expensive again. Towards the east, the land price decreases - for example [Kürten / Lindlar / Overath]. But then pay attention to the terrain, because building on a slope costs a premium again and public transport is somewhat less frequent.