As for the food portion of your post.

If the phase 3 DN isnt going down by time the spiders/rooks pop you're behind the eight ball a bit and dps is part of your roadblock. In my opinion anytime a lack of dps is part of the equation for wiping then the dps should absolutely be using food. The only time id advocate not using food would be while first learning the actual mechanic. You know the mechanic, now its time go use whatever resources to pass it.