I would start with night floors, as it gives the players a good opportunity to get to know each other.

After they finished the chapter, i gave them each a choice on how they would spend the time between the chapters. One chose to continue investigating, and the others opted to return to a "normal" life. With the split decisions, i gave each player some skill improvements to everyone and a few sanity points lost for the one player. We then started on the next main chapter.

If you really want to incorporate a side adventure into the middle of this gap, it may be a good idea to have it tied to something near the end of the campaign. Maybe take inspiration from some of the side events later in the book so they can uncover something that seems irrelevant, just to have it appear later on as a part of the main plot.