I think it's important to bring out the chemistry between the characters, author.
In fact, these days, I don't see the MC seeing more than a younger sister or Powder seeing him as more than a cool wizard brother.
Caitlyn has more romantic potential, plus their dynamic would be interesting.
A question: Now that Finn has access to the magic of time and space, a question has arisen in my mind... Did Belos/Philip meet Finn in the past too?
I doubt he would let Luz travel to the past without his presence.