The game does encourage you to mix the Fates black and white sets. On top of that, it's not too difficult to run mixed color decks since the rules aren't too strict about how to use them.
As for pacing, I find that it mostly depends on how you decide to play. In my opinion, not a lot of decks cater to defense, but it's more on how you use your deck that can be good for defensive play. I've had games that ended pretty quickly (in about 4 turns each side), and games that went on to upwards of 7 turns each.