The CWAL Rubber Room
"THE POWER OF GRORX COMPELS YOU. THE POWER OF GRORX COMPELS YOU." - djmmm
The Expanse is laid out as a trilogy of trilogies, in a sense. 9 book plan, 7 have been released so far. Each individual book has a mostly self-contained story, and each set of three books also forms something of a coherent unit.
They've been pretty reliable about annual release dates (COUGHCOUGHGEORGERRMARTINCOUGH). But if you want to be as safe as possible, you could read the first six books and then stop until the series is done. Book seven kicks off a distinct new phase of the story and ends in a cliffhangery place.
I would say you can go ahead and start reading it. There is a long term story arc covering the whole series that is very slowly playing out, but for the most part each story wraps up it's issues by the end of the book (with a few small exceptions).