Resurrecting this for a couple of proposals. I'm playing some games now and I'm finding the Ancient Era is pretty unforgiving at the moment. Past that, things are fine. I'm getting an excellent lesson in the usage of Walls to maintain order.
There are two things I would like to add:
+3 local stability from Village Hall and all upgrades. This is a starting point. 3 stability will mostly stabilize a city in a small empire during the Ancient Era without a religion, without Slavery, with a good-size garrison and no problems with unhappiness (tough to do!).
Raise the cap from stability from garrisoned units. There is a stability bonus from garrisoned units; it's a power function, so you get diminishing returns from more units. However, there is a cap. The cap is 10 points of stability if the city is getting instability from nationality, and 15 if it is gaining stability. I would like to raise these caps by 5. Taking advantage of this requires committing lots of units to long-term city garrison duty, so I think it is a fair trade-off.