Five is Plenty
I thought the first second and third books about Shiloh were fantastic. I also think the fourth set holiday cheer all around the world. So I suggest to make a fith. Marty is older and Shiloh has an adventure of his own! That’s the plot of the 5th book I would suggest. A 6th? I’m not sure but 5 is plenty thanks! And have a good time.
I’m just delighted that you loved the Shiloh books so much, but actually, I think that four books is plenty. I enjoyed writing those books very much, but there are so many other kinds of books I want to write.