1. How does the Vorkaufsrecht (right of pre-emption) work?

How the right of first refusal works and how differently the districts act is explained here! https://iniforum-berlin.de/2020/10/das-vorkaufsrecht-in-der-praxis/#more-2206
If you have received questionnaires from your Bezirksamt (district office), you should fill them out and send them back as soon as possible. They are very important for the so-called Wirtschaftlichkeitsprüfung (profitability check), which cooperatives also have to do. Simply put, a Wirtschaftlichkeitsprüfung is used to determine whether the purchase is worthwhile.
The Wirtschaftlichkeitsprüfung is only possible if the district office receives the information from all apartments in the house. Therefore, help your neighbors to fill out these forms – many people do not realize that most of the data is in the lease contract. In the districts it is now regulated that in each case two housing companies examine whether they want to step in as a so-called third party. You as a house community can also send cooperatives or the tenets syndicate your data in form of a portfolio and they can check whether the house fits to them.
If you have not heard from your district office, even though your house is located in a Millieuschutzgebiet (protection area), you should actively and persistently approach the building councilor and exert pressure. In some districts these offices have different names, for example “Amt für Stadtentwicklung” (Lichtenberg) or “Abteilung Immobilien, Umwelt und Tiefbau” (Steglitz-Zehlendorf). Start at the same time to determine the required data – time is running!