Here is a site where they go over some of this quickly.
the relevant parts you are specifically asking for are
Town and City Population: How Many In Those Walls?
For purposes of this article, settlements will be divided into
Villages, Towns, Cities and Big Cities (known as "supercities" in the
parlance of urban historians).
Villages range from 20 to 1,000 people, with typical villages ranging
from 50-300. Most kingdoms will have thousands of them. Villages are
agrarian communities within the safe folds of civilization. They
provide the basic source of food and land-stability in a feudal
system. Usually, a village that supports orchards (instead of
grainfields) is called a "hamlet." Occasionally, game writers use the
term to apply to a very small village, regardless of what food it
produces. Towns range in population from 1,000-8,000 people, with
typical values somewhere around 2,500. Culturally, these are the
equivalent to the smaller American cities that line the interstates.
Cities and towns tend to have walls only if they are frequently
threatened. Cities tend to be from 8,000-12,000 people, with an
average in the middle of that range. A typical large kingdom will have
only a few cities in this population range. Centers of scholarly
pursuits (the Universities) tend to be in cities of this size, with
only the rare exception thriving in a Big City. Big Cities range from
12,000-100,000 people, with some exceptional cities exceeding this
scale. Some historical examples include London (25,000-40,000), Paris
(50,000-80,000), Genoa (75,000-100,000), and Venice (100,000+). Moscow
in the 15th century had a population in excess of 200,000!