I consider your books as a “story.” If that falls into the “series” category, then I suspect they are a series. And as far as I’m concerned, you can write as many books in the “series” as you want! I don’t get tired of the characters. Which, to me, is essential.
Keep going!
Oh, lord!
That story has been told and retold! Where could I possibly go from there except into a Heinleinian folded space where characters from disparate stories meet and conflict?
.
Or meet and go on another adventure?