Sorry for the slow reply, I've been getting ready to run the game at a convention this weekend.
I think 1-3 players is the sweet spot, but 4 and 5 also work well. At five players you Skill Specialisations and Subtle Manifestations start to double up.
I think early teens an above is the age range. If you'd let your kid watch Dark Angel or Terminator unsupervised, they are probably old enough to be playing this game.
I would argue that all my work has Queer themes by virtue of me being Queer, and that's definitely true of this game. However, there aren't like mechanics or powers related to that. The game explores ideas of self expression, found family, abusive childhood, and running away to make a better life for yourself where you can be who you really are...There's also a bit in the back of the book about two prehistoric angels having a gay romance and being exiled by God, so I'd say it has LGBT content in it.
I hope that helped answer your questions, let me know if you have any more.