Like something is completely broken in this mod. Now I can't even recruit Cohortes Vigilum in the Italy region... they have just vanished from recruiting options.

The mod has numerous bugs, several of which I've noted. Some of them have to do with the pack file being incomplete, however being that I was playing as Koinon and Macedon it's understandable that they just haven't finished those factions. However for Rome to have issues when it was one of the primary factions of the mod, I would ask about it on TWC or their Discord if you don't get any answers within a few days here.

You can recruit them from one of the tiers of the Divided Assignments building chain. Roman legionaries can only be recruited from certain areas:
http://www.twcenter.net/forums/showthread.php?696026-NEW-ROMAN-LEGIONS-2-0.
What's more, you cannot unfortunately simply upgrade your Republican units (Principes, Hastati and Triarii etc.) into the Marian ones, you have to create them from scratch.

In regards to Rome and Italy in general, recruitment from there does seem to be bugged unfortunately, I was unable to recruit legionaries there. Your garrisons from all provinces however should return when you research the subsequent military technology following the Marian reforms.

Confusing, I know.

can you please tell me how do i achieve legionare units? how do i research marian reforms? step by step? thanks