Hello! Thanks for your comment and your interest in Thousand Empty Light. Great to hear you're going to feature the module - looking forward to it. To answer your questions:
1. [-] means roll with disadvantage, [+] means roll with advantage. This is also how the core Mothership rules styles it in its tables.
2. It should be fine to play the soundtrack underneath speech in your video. I agree, I think the music is excellent and I'd love more people to hear it.
Feel free to post the link to your video here when it's live.
Thanks again!