CDJs don’t support FLAC. Lossless is a useless waste of space for DJing anyway. Rip everything to iTunes with the computers CD drive, and use the iTunes Bridge function in Rekordbox to import it (allows you to browse iTunes from within RB). Use Audacity or a DAW for the vinyl. Encode it all in 320k MP3/AAC or WAV if you have space you want to get rid of, and everything should be seamless.
