Flashback, and new characters

I was never happy with the way the relationship with the client was detailed in the original so I've introduced a flashback section in Chapter Three, which had originally been handled partly by way of exposition, and partly by way of follow-up phone call from client.
I'm also introducing two new characters in this chapter: one, an ex New York cop buddy of Hans, who recommends him for the job; and secondly, Van Buren's loyal secretary
I may decide later on to move this Chapter to the beginning of the novel because as much as I don't care for detailed expository sections, neither am I much of a fan of flashbacks.
But at the moment I don't think this flashback section will upset the flow of the novel too much.

I'm conscious of the fact, also, that, although I still have the plot of the original novel in my head, and the scene and character details, this may only be the first of a number of deviations from the original.
I'm also conscious, though, of the need to finish each chapter with the reader wanting more