How can I automatically add files that are in the inbox node to the library?

[PeidosFTW]

Is it the same for adding those files to the now playing section?

[Steven]

I am not sure what you mean exactly but you can configure musicbee to add files directly to the Library instead of adding them to the Inbox. Check the Preferences/ Library settings or on the Manual Rescan Dialog if you add files manually using the file scanner dialog