OP, I think most of the suggestions in your post are really good. But please never, never, ever have a tech cost increase per city again. To put the brakes on expansion, you could introduce very light maintenance per city, or have district costs scale with # built, or have amenities kick in sooner and more harshly (if cities required amenities at pop 1, that would nerf ICS quite a bit). But please no per-city tech penalty. I want to build empires in this game!