I wouldn't recommend making a samurai one of your first awakenings. Katie is a good choice, her passive will help a decent amount and her increased stats will make her even more of an all round tank that makes heavy armours for lower hitting enemies pointless. She's a solid choice that you will use most of the time.

If possible, i'd say go for an archer next like Spica. Archers, once awakened, will deal extra damage to flying units and Spica especially also grants other archers more damage. That said, out of your choices i'd go for Iris or Mehlis second. Iris on deployment heal can be rather nifty.