Right now in my seleucid campaign, my population was exploding so i've throttled it. I've deleted baths/sewers and build all the public order buildings I can. I set all small towns that I have no major interest in to AI financial build. And I am letting the AI adjust my tax rates. MOST of my cities have hit critical mass around 15-16k and are cranking 2-4k denarii per turn. I've allowed some cities to expand to 24k, these are all universally losing me bug money but I need them for troop production.

It seems the happy medium is to allow squallor to get high, and counter the effects with temples and what not. So far its working well for me.