On the question of razing cities or keeping them: this is indeed a crucial question, since on Demigod and above the AI usually has acquired such a huge culture lead over you, that conquered cities flip back quite often. There are two ways to deal with this problem:
a) Just raze the conquered cities (gives a lot of free slaves...) and bring your own settlers to settle the freed up territory.
b) Keep the conquered cities. On the turn of capture you can fortify your units in it to quell as many resistors as possible (cities never flip on the first turn), but on the next turn move everybody out again. It's very annoying to lose half your army in a culture flip... Then strive to eliminate the civ completely as fast as possible. Once the civ is eliminated, the cities can't flip anymore, and you can safely use them.
Both approaches have advantages and disadvantages, and it depends on the circumstances, which one is best.
a) allows you to make peace at any time (if the original objectives have been achieved, our the war starts going badly and you need to recover/consolidate). But other AIs will get furious at you because of all the razing. And you need to build a lot of settlers, which I often try to avoid.
b) Requires you to "go the full distance", until the civ is completely eliminated, so the campaign better be a success... Also you need a few units in reserve, which can re-capture flipped towns and keep the supply lines open. So warfare is a bit more difficult. But the benefits are also big: a lot of population that can sooner or later be used (as productive cities with already existing aqueducts, marketplace, harbors, etc., if the captured territory is close to your core (or you manage to rush the Forbidden Palace there), or as "science farms", if it is not). Also you can keep any Great Wonders the AI may have built.
a) Just raze the conquered cities (gives a lot of free slaves...) and bring your own settlers to settle the freed up territory.
b) Keep the conquered cities. On the turn of capture you can fortify your units in it to quell as many resistors as possible (cities never flip on the first turn), but on the next turn move everybody out again. It's very annoying to lose half your army in a culture flip... Then strive to eliminate the civ completely as fast as possible. Once the civ is eliminated, the cities can't flip anymore, and you can safely use them.
Both approaches have advantages and disadvantages, and it depends on the circumstances, which one is best.
a) allows you to make peace at any time (if the original objectives have been achieved, our the war starts going badly and you need to recover/consolidate). But other AIs will get furious at you because of all the razing. And you need to build a lot of settlers, which I often try to avoid.
b) Requires you to "go the full distance", until the civ is completely eliminated, so the campaign better be a success... Also you need a few units in reserve, which can re-capture flipped towns and keep the supply lines open. So warfare is a bit more difficult. But the benefits are also big: a lot of population that can sooner or later be used (as productive cities with already existing aqueducts, marketplace, harbors, etc., if the captured territory is close to your core (or you manage to rush the Forbidden Palace there), or as "science farms", if it is not). Also you can keep any Great Wonders the AI may have built.