We are also very young (26 29) and have acquisition costs etc. of 610,000 including the land with a lot of own work. Normal semi-detached house without a basement, 140 sqm living space.
What you can already pay attention to now is that the plot does not make the house unnecessarily expensive. For example, avoid a hillside or slope, short access roads, easy development, no "lake" (depression with water), possibly favorable south-facing orientation for a standard floor plan. - Things like that.
From BW or IN BW?
Two years ago, we were at 560,000 € for 170m² plus basement and outdoor area and everything that goes with it ... almost in the middle of BW
In BW, 2-3 years ago everything was still okay, but now everyone here is going crazy. New build apartments in rural areas with 130 sqm are priced at 590,000 here.