There is a large bundle of documentation. Including a detailed BOM, shopping carts for various distributors, sample code for your own experiments, etc.). Here is an overview of the required components in advance. All components are easy to get. The BOM also contains replacement types for the critical components (relays, transistors, Zener diodes). All of these components cost between 40-60 EUR in total.
BOM:
Capacitors: 100uF, 22pF, 100nF, 470nF, 220nF
Sockets: ZIF32, some socket header for Display, DC/DC Modul, pin header for ISP