I'm in the middle of reading Book 4 of the Vanguard series.
Off the top of my head, these are who I'd cast for various characters, in no particular order:
Arlene Tur - Captain Khatami
Powers Boothe - Cervantes Quinn
Martin Sheen - Tim Pennington
Simon Fisher-Becker - Ganz
Lena Heady - T'Prynn
B.D. Wong - Ming Xiong
(An older) Esai Morales (with a caesar haircut) - Commodore Reyes
Rekha Sharma - Rana Desai
Rutina Wesley - Ana Sandesjo/Lurqal
Sam Waterson - Zeke Fisher
That's all I can come up with right now.