Well, I'm a bit stuck at the moment, because I'm yet sure how to proceed. Also a rather busy with other stuff.
But let's answer a few questions

To define the angle of the buildings alone would kill my nerves. Gosh, how you doing this? Or is it 'just' intuitive?
Are you drawing this in an oblique perspective? I ask since I see the ruler and protractor out.
I don't really know all that much about the differences between the various types of parallel projections. I saw a wikipedia article once, but didn't get the gist of it I suppose if it's any kind of projection, then oblique is probably closest, but I don't really bother much with working out angles and line lengths. Basically, I just draw the footprint intuitively and then I draw the vertical lines going up. If I'm happy with it, I ad a few details. The ruler/protractor I mostly use for drawing good parallel or perpendicular lines.

(1) Something as grand as that couldn't have been built in a day - and hopefully, the end result will underscore that specific point. I wonder what architectural changes occurred, over the life of that collective construction project?

(2) What is that on the right? A dam or an aqueduct of some sort? There's water flowing out of it. Where's it coming from? A river? A lake? An underground spring?

(3) Where are the gates of this walled city? I'll be that they are truly something to behold?

(4) I like the irregularity of the trees on the right near the water, more than I do the regularity of the houses within the walls. Were there building codes in those days? Were there housing subdivisions? Was the project one grand design, like a blueprint drawn well ahead of time and thought out in a very detailed manner? Who built it, and why?
Wow, lot's of good questions. Thanks for taking the time to think about it and ask
Ad 1) It certainly wasn't built in one day. My idea of its history are very sketchy. It was originally built by something of a lost civilization. The Roman-like buildings are all that is left of what these people once built and these currently house government and courts of law. The first humans to settle the remains built the walls and large square towers, ever expanding as the population grew. Eventually there wasn't enough room to expand even further so the rich and powerful started expanding up, building taller towers to outdo the others. This was during the heyday of this city, when it was the capital of a rich and powerful kingdom, called Firin-Iradas. In time, every square foot of ground was occupied and the city relied on its surrounding lands for food. At that time, the city was pretty much an impregnable fortress. Eventually, the power of the kingdom waned, and other kingdoms conquered the surrounding lands. In the end, Galastan was conquered not so much by siege or direct assault as by starvation. The city's isolated position meant it was completely cut off from its food supply and its king had no choice but to surrender.
Later a huge fire devastated much of the 'normal' houses in the city. They rebuilt, but the style is more in keeping with the architecture in the rest of the kingdom (the smaller houses with the pointy roofs).
Nowadays the city has lost most of it's military relevance. It's location in the nation is not of strategic importance and defense is no longer as important as it used to be. A lot of the towers have been converted to housing, with the rich renting them out to the lower classes.

Ad 2) nope, it's more of an outcrop with walls on three sides. I hope to make that more obvious when I work on it in photoshop. The water comes fromn a spring higher up the mountain and is led through an aquaduct to a cistern behind the row of houses on the top (not visible). After that it pours out into the park below.

Ad 3) there already are three One is in the lower left corner (in pencil). The other two are on the inner ring. One on the left, still mostly in pencil, with a causeway leading up to the gate. The other one is the double tower in the center. Most of these gates are huge towers with very narrow entrances. The gate to the castle (not yet drawn) is going to be a lot larger, but that's one of the things I'm still not sure how to do.

Ad 4) the parks are meant to break that monotony up a bit. I don't know of any housing codes or blueprints
This is quite a tricky bit. I wanted to have some distinctively different style for the older buildings in the city, but that kind of architectural awesomeness is quite beyond my skills, so I decided to keep it simple and square. And BIG.