Trading Post: I would save up for the next rotation. Artillery officers are fairly niche units, and your team is barebones enough that you'd be better off grabbing another more general-use unit. I consider Chydis or Saki better overall. This depends on how many DCs you have saved up, but I imagine you don't have that much.

For Awakening, I would say Spica first, but since she's pretty far off for you I'd recommend AWing Katie since she's always useful. My recommended order would be Katie, Spica, Iris.

For the future, you definitely want to look into getting a strong tank because what you have currently won't cut it on the harder missions.