The size of the city was somewhat planned, though they usually expanded beyond their original designs. Here's a nice image of the plan of Alexandria in Egypt, though that would have been pretty elaborate as far as designs go, since it was planned to be an important city.

A lot of Greek settlers went out to settle in new towns. Many of them were veterans who were granted land in/near these new cities after they finished their service. Others might have been exiled from their original cities or deported. Natives of the conquered land would also be resettled to these cities, and probably made up most of the population. Wandering merchants, who often followed Greek armies around on their campaigns, might also settle in these cities.

Soldiers usually helped build the cities, but they may have had slaves/prisoners of war help as well. The roads would be put down, then maybe a civic building or two and a temple would be built.

There wouldn't have been too many architects, city building was based more on surveyors, who would lay out the roads in a grid then move on to the next town. It would be the rulers of the cities who would commission architects to build acropoli, temples, and other civic buildings to gain the favour of their citizens.

These towns were established as 'city states', so they were largely self-governing and were intended to be permanent. It probably didn't take long for them to be seen as a city, as they were designed to be cities.

My sources are "The Hellenistic World" by FW Wallbank and a multitude of primary sources that I read for my Ancient Greece class last semester.