Here's a suggestion. Why don't we just make a list of buildings each faction is likely to build and later worry about which units gets built by what. Since almost every building mentioned in the source books are specific to a particular unit I think it'll sort itself out. All we need is, lets say 20 special buildings per faction and then just take it from there.

Since the source books only superficially go into the economy required to reqruit each unit, there's IMHO no point dwelling on it. We have to make it up.