Yes. rekordbox 5 follows all the functions of rekordbox 4.
Yes, you can use devices with tracks exported in rekordbox 4 or earlier with rekordbox 5 as is.
You cannot load Track Libraries from applications other than iTunes directly, but you can load Playlists, Cues, and beats and tempo information from other applications if you convert them to rekordbox.xml format first. For details on rekordbox.xml format, click [here] (http://rekordbox.com/en/support/developer.php "").