Hi, I checked all items in your description, the assetsyou have shown as example is heavy, about 700MB, if this size is suitable, I can create a city like that, and optimize the materials for it to make it with less filesize, I know some tipe to reduce the volume but still have a good result, for example in the gas station you have designed, you can remove curves and have vertices lowered by 20 percent, same for maps.
But I have another suggestion too, there are plug ins that make city automatically, I have used some for previous projects. Let me show samples of them, if you like the quality then we can easily create many cities created automatically.