I'm not sure what the optimal number of cities is, but it's almost certainly 2 or 3.
after the latest patch you can do 4 cities efficiently if you have the locations available, which is admittedly p rare on diety but 3 is a good sweet spot for cultural games. not settling that third city (and your choice of city location for the second city) was probably the biggest mistake you made in that first persia game imo
in the latest game i don't think you have a legitimate 'good' third city spot that won't provoke the AI and the only open land is fairly resource poor but even despite that i probably wouldve built a third city on the coast (since those whales are going to be grabbed by your cap eventually) because i think its easy to generate enough culture mid to late game to exceed the increase in policy costs.
after the latest patch you can do 4 cities efficiently if you have the locations available, which is admittedly p rare on diety but 3 is a good sweet spot for cultural games. not settling that third city (and your choice of city location for the second city) was probably the biggest mistake you made in that first persia game imo
in the latest game i don't think you have a legitimate 'good' third city spot that won't provoke the AI and the only open land is fairly resource poor but even despite that i probably wouldve built a third city on the coast (since those whales are going to be grabbed by your cap eventually) because i think its easy to generate enough culture mid to late game to exceed the increase in policy costs.