Buy now or wait a little longer?

I myself am active here in Berlin and the surrounding area and would advise you as follows:

1. You should definitely look for and buy a plot of land free of developers now. The timing could not be better. The supply is large, but due to the immensely increased financing and construction costs, the demand for plots of land has collapsed, and prices have therefore fallen significantly over the past two years. The standard land value should not have to be exceeded; depending on the offer, you can even negotiate the price down by 10-15%.

2. After purchasing land, look for a small general contractor-masonry builder from Brandenburg. They all currently have available capacities and are happy about any building interest. The prices currently offered to me by several companies amount to €2300 ready to move in with completely free floor plan design. That means without floors, painting work, and patterning (shading is expensive...). Including additional construction costs, you can easily get by with €500,000 for 160 sqm. Brale and Rostow are significantly more expensive, Town & Country as well, plus inflexible.

Where would you preferably like to go? Does Pankow mean the district or the neighborhood?

Apart from the quite impressive figures, I am asking myself a question here:
How will land prices probably develop?

I would assume that those around Berlin will still rise in the next 10-15 years, and stronger than inflation. That would speak to me in favor of buying the land now (as long as there is no building obligation). And if the house is only built in two or three years, that would not be bad.

Especially with the rental prices. If you were somewhere out in the province right now paying a few hundred euros rent, that would be different. But like this?
250k equity. Monthly savings rate of at least €3500 with €1500 rent warm currently. Salary increases very likely. That sounds very solid to me now.

Nominal interest rate: 3.68% / Effective interest rate: 3.76% for a loan amount of 600k and an interest rate lock-in period of 10 years.

Thank you, no, it is more meant as Pankow as a district, so Pankow, Ndsh, Rth, Wilh. and possibly Franz. Buchholz. I know, that is very limited but we are in the comfortable situation of not having to move at all costs with a 100 sqm apartment.

My suggestion would be: Take your parents' equity with you and find a plot of land and pay cash on the spot. That way you have an unencumbered property and later free choice of bank. Otherwise, it will be more difficult to find a bank for the house financing that might be cheaper than the land bank.
Then you pay back the equity to your parents over the next 2 years. In the meantime, you can already look for a suitable house in parallel that you want to have built. When you are unencumbered again, you go for the big loan with the house. By the way, €500,000 is not unusual here.