To make cities, maybe apply some visual synecdoche? Make a part signify the whole. You could make the size and number of buildings represent population size, so a hamlet is one little cottage while a city could be two timber frame houses and a tower. I think making isometric buildings that match your current style would look great.

cheers,
Meshon

Edit: Oops, I should have looked at that tutorial, that's great! Are you looking for something in a different style than that?