How/when do you start building your walls?

I trying to learn the basic build orders to become a better player, but one thing all the basic guides don't include is how to wall effectively in dark age and early fuedal.

• How many vils should I use?
• What resources should i take them off?
• should I make extra vils to build houses/walls
• How big a section should you put down at a time?
• What military buildings/ large building should be in your wall?
• What is a good time to start walling?
• How big should you walled off section be?
• When to use stone walls vs palasades?

Any additional advise on walls would be appreciated.