Actually, I think the Vostroyans use carapace armor, so I think you should drop the light infantry and take carapace armor. If you could take more than five doctrines, this is how I'd represent them. (after reading Rebel Winter)
- Priests
- Enginseers
- Conscript Platoons
- Die Hards
- Iron Discipline
- Veterans
- Carapace Armor
- Close Order Drill or Hardened Fighters
Of course I've only read one piece pertaining to the Vostroyans, so I don't know how accurately that would represent them. Pick and choose from that list though.