Can anyone suggest ?

You can use smart playlists in iTunes and import them to Rekordbox via bridge. The best way is to keep all organizing on one platform otherwise it will get messy very quick. I have one "Rekordbox" folder in iTunes that contains subfolders, playlists and smart playlists. Every time I add a tune I delete the whole playlist library from Rekordbox and re-import the main folder via bridge. Only takes a minute and gives you a lot more sorting options.

^^What he said.  I recently started using playlist after I lost all my playlist via icloud match.

Very easy to work with.

We've made suggestions to add a "Smart Crate / Smart Playlist" addition to rekordbox.

Personally, I keep two copies of my raw audio files - both on separate drives so that I have a backup. The first is categorised by (folder) in Genre - the second is categorised by Artist. I keep only the tracks that I know I'll need rekordbox'ed on my laptop - organised in playlists by Genres (and other custom labels). If I need a track from the harddrive, I can connect it to my third CDJ during a gig and drop it in.