Nice little guide. I like your design philosophy, about thinking the history of the area into the level. I plan later on to make a town that has been sacked and then rebuilt. So there will scorched and ruined sections of the old city wall, that poor people have tried to incorporate as walls of their squalid homes.
Another thing one can contemplate about is the climate of the area and time of the year that it is supposed to be in.
I'm currently making a rocky island, set in a temperate climate zone and in a late winter season. This means no jungle stuff and blooming vegetation, but rather leave-less trees and bushes should dominate the land scape.
I'm actually planning to hold a siege (If the players can't dance around it somehow, love being surprised as a DM.) throughout the entire city, including upon the walls in certain places. Though one could start to wonder, haha.
