@Richie > No worries - it's a learning process for the veterans too. ;)
1) Correct, it only backs-up your database files. If you want to move it to a new Mac, your best bet would be to use the migration wizard (Mac software) but alternately you could simply use an external drive and use that as your source for the audio files. You should transfer the library to the SAME location on your new Mac and then copy to database.
2) iTunes can handle that for you prior to importing them into Rekordbox. It has been suggested to add a duplicates finder to the software.