You can check your back up for the first import to the hard drive. As to the easiest method for the second importing, you can do all at once or drag folders in as a new playlist so your not remaking them. Yes going from a mother program to Rekordbox does have some work in it, but worth.
You can also look into Rekord Buddy and see where he is with 2.0 which will move Serato into Rekordbox. 1.0 moves Traktor.