Rekordbox imports from External USB to sync with itunes drive

The big question after I lost my backup is...

Before I was using itunes with Rekordbox, and the itunes library is on an external hard drive, now I have to start anew. 

I found the official guide to reimport playlist from my 1TB usb, which has most of my music. 

Before I proceed, I have a few question...

I am able to relink my itunes library, but should I click "Do Not Copy" if I do not intend to store the actual songs on my Mac hard disk? 

After importing playlist with Do Not Copy, what does that mean? I do not think that the imported playlists in the rekordbox is playable without linking to the actual music files stored in my Itunes Library, so what should I do to sync them?

Please help!