Is it possible to migrate existing forums?
I tried by exporting all the "sf" tables (such as wp_sfposts, wp_sfoptions, etc) and then imported it to local database for testing but it doesn't seem to work. The forum page loads but it doesn't show any forum content. And also there are no errors logged.
It depends on what you are trying to do. From what your are writing it sounds like you want to set up o local testing or development server? If that is the case we would strongly recommend you to do a full database dump on your live server and import it locally. When that has been done you need to use a plugin like "Better search and replace" or WP CLI to search and replace the hard coded urls to your live server and change them to whatever your local development setup is called.
And if the above is not what you are trying to do, please let us know and we will do our best to continue helping you.
Joakim @ Simple:Press