How much specialization?

[yesdachi]

In the beginning it is usually a bit of a scramble but once I have established a base of provinces I start one going after knights, swords, spears, archers, ships and sometimes siege but I usually just buy them (mercs). Overlapping is ok too; a province that can build a variety of units is handy.

Whenever I have a break in building the main focus (need a castle upgrade and don’t have that much $), especially spears or any units that have poor moral, I throw in a religious building for the moral boost. Armor too. Or once I reach the top I go back and armor and church up.

Later It depends on what lands I conquer and how many fronts I have.

Usually in a conquered land if I am just a building or 2 away from being able to make a cool unit I build up to that level, if $ allows. Weather I need the units or not. I just like to have them available.

When I am doing well I build just about anything but especially farms and trade buildings to get $ and those great builder, steward, trader virtues for King and Governors.

[sunsmountain]

It depends on the faction. Look at the faction's top units and note down what they need. Then work towards that goal.
If, on early, you already have a fort somewhere, chose that province to be your chivalric knight producer (if catholic), meaning royal estates, horse guild, armourer IIRC. Building a fort requires 4 years, and its nice to use your starting resources to your advantage.

After the first 4-5 provinces, the rest of my provinces concentrate on farms/trading/mines.

[squidums]

Early in the game when cash is short, I have 6 or so specialized provinces (cavalry, infantry, archers, 2 for ships, politicals).
Which provinces I use depends upon what i start the campaign with, valor bonuses and iron.
I also specialize the provinces with decent raw incomes for farming, and those that can I specialize for mining.
I am always building, how much depends upon my income.
I try to balance between building for better troops and building for a better income.
When I have enough cash, I build in other provinces to increase loyalty, so that I can increase tax. I try not to let any province fall below 140% loyalty. Once there is enough money coming in I can usually keep most provinces at 200%.

[tigger_on_vrb]

It very much depends on the faction - look for resoures, good farming provinces and especially regions that give the +1 valour bonus. Dont forget about establishing a trade network! I agree with what the other posters have said - heres some thoughts of my own
The easiest buidling to get to master level is the horse breeder and +1 valour mounted units are very useful near the start. This is most true for the turks - get Amenia pumping out +2 valour Armenian heavy cavalry and +2 turcommon horse when you get that egyptian province.
Also If you are the Spanish for example build up one province for infantry without the armour upgrades for use in the desert.

[ichi]

I also have a tendency to build up a lot of provinces - I like to have a province dedicated to making one of each type of unit: spears, swords, cav archers, heavy cav, light/medium cav, spies, assassins, religious types, emissaries, artillery, and a couple to build ships.

Early in the game I try to tech up at least five provinces - ships, agents, infantry, cav, and missiles. I choose which province builds what based on province bonuses and upgrade abilities. I like to get my missile troops built in provinces with iron so I can armor them (this is different from most peeps I think who armor their melee troops).

I also build all of the economic and happiness buildings in each province.

Towards the end of the game I can produce a full stack of various units in one turn.

ichi