City specialization is not a good concept to learn empire development.
Food is king indeed:
You want to incorporate as many

specials as you can, as fast as possible, in order to increase the power of your empire (citizens

)
You also want to be able to control the game strategically, by having cutting edge technologies.

comes from

which is the reason why you want to plant a few cottages on the way.
(I like the rule of thumb from
@bigbamboo : 2 cottages/city is a reasonable goal when looking at early war games)

is a "residual" resource that does not matter until you have a decisive weapon to build. (examples: an archer to defend the city, a cuirassier to

some nearby civ, a united nations to govern the world, etc...)
From there on, every city pretty much develops the same way:

>

>
Only mature cities deserve some special buildings that will give a good return on investment.
- Example one: a library in the capitol because it has lots of commerce
- Example two: a national epic in some city that has lots of food.
This does not mean that the capitol is condemned to producing science only, or that the national epic city has to prioritize great people production all the time.
City specialization belongs to the realm of anecdotal tactics and should not be much of a concern when leveling up in this game
