I haven't checked in for a while, but it looks like you've been busy. I had a similar idea with the armies, I was less focused on making them unique to the Civ/Culture Group though. I was thinking of starting out with an Army unit (which is equipped with stone armaments) immediately, then have that upgradable to an Army with bronze, iron, steel, black powder, gunpowder, etc. Basically, other than a few specialized units like Scouts, Siege units & Settlers, for example, I only wanted 3 primary military units: Army (land,) Fleet (sea,) Squadron (air.)
Regarding your culture groups, that does sound pretty good, however, the first thing that came to mind for me was - what if a player never meets requirements to unlock any assets? They'll just forever be a Tribe?