I solved it on my own - if someone is interested in the answer, here is my way of doing it:
-Multiple realm creation-
· Re-run the CMake configuration step and change INSTALL_PREFIX to a destination of your choice. The directory specified there, will be the 'home'-directory of the new realm.
· Make sure to add -DTOOLS=1 to the configuration again, as you need to start an own worldserver for each realm
· Run 'xcodebuild -target install -config Release' in terminal
· Create own world_<your Realm> and characters_<your Realm> database via MySQL (I modified the provided create_database.sql file) and import the .sql files, like when setting up the first realm (download TDB for world database and use .sql from 'base'-folder for characters database)
· Add your new realm in the auth database inside the realmlist table
· Go to the 'etc' folder of your new realm and customize the worldserver.conf fitting to your new realm -> realmID must be set, database logon information, port (must differ from other realms), data directory (maps etc.), [...]
· You can delete the authserver.conf, if you want to use the authserver from your first realm. Only one authserver must run for all realms to handle authentication.
· Start up worldserver in each 'bin' folder of your realms
· Start up authserver in the 'bin' folder of the realm of your choice (where you have configured authserver.conf correctly)