Thanks THW, always full of wisdom. I'll find some old maps of both those cities.

The turtle is several miles across I'll call it two wide by three long in none submerged area. Its shell is thick enough that fire short of burning the city down doesn't much catch its interest (should that happen it might decide to put out the fire which would be bad for the citizens and makes a good cautionary tale for what happened to another turtle city). Fuel wise and building wise they are reliant on it coming close to shore periodically this has the down side of meaning its not always available and the upside of not exhausting the resources around it quickly and having to import them from further and further away. The inhabitants were originally land dwellers so their building style is what they know wood and stone. The turtles shell is many feet thick, and though you wouldn't want to put in a lot of basement sinking support posts many feet deep doesn't catch its attention (I was picturing it as having something between an actual turtles shell and an earth like crust).

Farming would be limited to the areas between the "hills" were enough dirt has gathered and insufficient for the support of the city . Fish is as mentioned abundant for the dwellers of the city, the rest of the food must be imported. Your points make me think that I should have the turtle frequent inhabited waters, which makes sense as it eats fish and the deep ocean is a vast desert from the biological perspective. Its always on the move seeking out the richest fishing grounds for its fantasy sized appetite. The light house is on the shell nearest the head as the head is mobile, dangerously bitey, and less constant in its vertical position.

The city started closer to the rear on the left side of the turtle (port side if you prefer) as a fishing village, the swirling currents where a great place to drag a small net to catch some of the dazed fish left in the turtles wake, just a poor place to land a laden cargo ship. The city spread forwards from there the population boomed and then through some political or economic nonsense I've not yet worked out (and would welcome ideas for), busted. Now its on the upswing again and folks are flocking to the city (or arguably just waiting for the city to come to them).

Water is the most problematic resource. Either I have to make the oceans fresh water(I'm from the great lakes and secretly believe all water should be unsalted anyways), have the turtle stay in high precipitation areas, sweat fresh water, or come up with some other solution that is more fun than hand wavey magic. I'm up for good ideas on this resource.

And yes Azelor its turtles all the way down.