i think the 4-5 cities plan is for the early game. they will be sufficient to get you to the mid game. what you do then depends a lot on how the game develops. if the diplomatic situation is stable, you can go monster hunting for fun and profit, perhaps aiming for a mastery quest victory, if your neighbors expand more, you may be forced to fight them and take some of their cities; this may lead to a conquest victory, or maybe a "diplomatic victory" (which really just means that you don't kill everyone - those who are smart enough to accept an alliance will be spared ) if you want a quick victory, you can research the spell mastery tech, build the towers and win. if there's plenty of room and nice spots, there's nothing wrong with forming more cities (about a dozen or so is easily manageable and profitable).

there really isn't one formula for winning, but quickly expanding to about 4-5 cities will at least get you out of the early game and into the stage where you form plans on how to proceed in the long run.

 

 

I pretty much do what Grand... says, with one modification. I will build a second 'fortress' on the best essence site I can find. 2, 3, (yikes, I found a 4 in my current game). The second fortress city is buffed up so my 'second' generation of troops have magical enhancements. Depending on timing, great mill may be here, often, however, it is in first fortress so it helps build the heavy buildings. Filler garrison troops (to keep monsters away from border settlements) will continue to be trained at the first fortress. But the battle line troops come from the second fortress.

The number of cities you will create (or keep) during a game, varies greatly on several factors:

Do you NEED a city there to block an enemy access & grab some important resources? (may imply you are willing to settle even on bad spots with no essence or low food / production)

Do you have a good spot for each type of city you need? (a high production city - fortress - near a forest and with some clay, preferable with at least 2 essences, a town with loads of food anything with 1 essence or more is good preferably near river / sea, and a 2-3 essence with decent production and food for conclave). 

Can you safely expand (no big bad Joe monsters roaming to waste all your effort, no warring neighbors nearby, it has a decent / good / perfect settling spot & resources) - your Unrest penalty won't kill you if you drop 1 more city.

Should you keep enemy captured cities? Do you have spells & mana to lower unrest to a decent level? Do you have the necessary money to rush unrest reducing buildings to turn it into a productive city and not cripple your Kingdom / Empire?

 

Usually Empires have an easier time managing more cities, while Kingdoms should stay smaller but more specialized.

Be warned that the conquered city will stay in strike (100% unrest) for several turns, and also increase (more than noticeable) the unrest in all your other cities. So if you're on the verge to discover a key technology that you really need fast, it may be better to raze it and rebuild