A deep interview with Arvo Pärt's wife Nora (for Estonian Televison, 40 minutes, with English subtitles): https://www.youtube.com/watch?v=zssKYgi-aHQ

Oh, and a documentary, "24 Preludes for a Fugue" by Dorian Supin. You'll maybe notice some of Arvo Pärt's quirky sense of humor there as well: https://www.youtube.com/watch?v=dRwTgme1_KE