Is Ocean of Stars the final installment?
Short answer: No.
Long Answer: Ocean of Stars precedes a larger part of Kennedy's journey. In fact, I never actually intended to write the story of Book 3 in the way it unfolded. The original plan was to start the timeline six months after the point where COTU ended...that didn't work out so well. I kept going back and revising my outline to include more flashback scenes, and eventually I realized I was skipping over vital developments. Sometimes these characters know more than I do. They want their stories told the way they want. *shrugs* Gotta give in to the creative process ;)
So how many books are you planning?
Short answer: I don't know.
Long answer: The story has to feel complete, and the characters need to have fully developed. At this point, there will definitely be a fourth, possibly a fifth. Beyond that, I can't say for sure. I've known from the beginning where Kennedy and Phoenix are heading, but I have no idea how many books it will take to tell their story.
Let me know if you guys have any other questions. I love hearing from readers!