If my calculations are correct, your map is 5 by 5 miles ? or 25 square miles.
and that is huge unless you intend to map the surrounding countryside and a few villages as well.
A city like this could fit in a area under 1 sq mile.

As too plan a city proper, I don't find it easy either. Xcali post is a start.
Cities emerge at crossroads where there is trade. But at the same time, markets are not necessarily in the center of the town.
You can find a lot of inspiration by looking at old cities, either ones that still exist or based on historical records.

One very defining characteristic of the city is whether the urbanism is planned or not. Most cities were not and many cities today, while having plans for the future, have a lot of constrains they have to work with.

I'd start laying down the main roads. These would be connected to the regional roads and serve as the entry points to the city. There is a good chance the main features of the city will be close to these roads.
Then you might have smaller roads around the city...

Landmarks, public places and other features would be located were streets intersect.

Markets, there would be several of them, spread across the city. Having a unique district center makes no sense in a world where most people travel by foot. There could a unique smaller specialized market but general markets are spread out. Your city would also have buildings and market right outside the city gates. The space being limited inside the city, they tend to spread outside the walls.

And that point can actually be a big concern. Having a wall limits the size of the city and can be seen as a disadvantage. Gunpowder changed the war and defensive walls were not what they used to be.
If the city is near a border zone with another country, the use of a defensive wall can still be justified but if it lies inside the country, maybe not so much.
Some historical cities like Carcasonne in France for example, saw the walled part of the city being abandoned by the wealthy and felt into disrepair and poverty overtime. Until in was restored in the 1800's.