GM:
You're much further than I am, just finished Levithan Wakes and honestly the 1st season on SciFi followed it so closely I knew everything happening. Though I do find that I did miss the extra characters the show added, missed seeing some of insights into the politics.
Do they show up in later books? I'm thinking of Chrisjen and Sadavir.
Chrisjen does. I think Sadavir does too but at the moment, I don't recall with certainty. The books do branch out though with several of the secondary characters bringing them into a spotlight.
I liked all the seasons and how the basically stay true to the main points.
I'm a huge fan of the show and a bigger fan of the books. I am so glad Amazon picked it up to continue the series.