First of all, I just want to know that I'm just a normal human being...
Therefore, there's might be some flaws in my judgement...
So, an early apology from me should compensate that...
Now...
On to the questions you had in your mind...
1. Since Kotarou and Kagari are connected (mentioned in the Terra route), let's just assume wherever there's Kagari, Kotarou will be there...As for how Kotarou brought the five girls, I thought Kotarou used some of Kagari's theories and equations to bring them from the branch worlds...
2. Esaka-san, maybe? Or Luis? Anyway, just think of anyone that K