Our website is one of the best known resources for ModSecurity and OWASP Core Rule Set (CRS) integration as well as Apache configuration.
There is a curriculum with up to 12 individual tutorials:
This will teach you everything around the setup of a secure Apache Reverse Proxy (Gateway Server) with ModSecurity and CRS on top.
Our security expert Christian Folini also offers courses that cover these subjects. You can choose between online and onsite courses.
There also used to be a translation of this curriculum into German and a minimal nginx / ModSecurity / CRS tutorial. However, this was discontinued. You can still find them on archive.org. You may have to look up the individual pages one by one on the archive.