Who to 5*?

I would personally 5 star the tharja, since you team lack a counter to hector, nino and other green units. especially with 2 blue units in your team and the lack of magic damage in the team.
To be honest, I would 5 star both and take out Klein. But I understand you most likely dont hae the feathers.
By the way, congrats on the nice iv's.

You might need to include some magic damage so I'd go with Tharja.

short response - Whoevers cleaning up the most. Probably Kagero - since most units in use are infantry

Tharja is more important, but the Kagero will help a lot with annoying blue units such as Linde. I'd consider Kagero a close second.