Can anyone tell me how much family gold is required before the option to buy the lordship of a city becomes available? And is it possible to do so on a rogue city not connected to any of your regions?
It is not possible to buy a city of your own realm.
It is not possible to buy a rogue city.
The amount needed varies per city, but is very high (probably in the 6-8k range, but I can't say for sure offhand).