The forum is set up and we are converting the 620.000+++ posts as we speak, and have begun looking into advanced settings of the forum.
We want the forum to staore data in MySQL database, not in file system, but this never came up as an option during install. Is it as simple as setting "MySQL" option in ACP and go from there? Hopefully setting MySQL also let us chose a methode for caching as well. This option is impossible to set to anything else than "No caching".

Qestion: Will the data now stored in file system convert into a given SQL DB when selecting this option?

If you create a new database file storage configuration, you will be able to switch some or all of your existing file storage extensions to use this new configuration, and the files will be moved in the background to the database.