I think 10,000 might be a little high for the total population. It looks like there are about 400 buildings here. Now some of the smaller buildings outside of the city would be granaries or barns, and some of the ones inside the city would be offices and warehouses, and not dwellings. Of course, within a couple of miles of the city there would be an equal population living in smaller farming villages and homesteads.

I would put the population at about 4-5,000, and as for the military, I would put the garrison at about 200 regular troops with another 200 as town guard/militia, and maybe another 300 that can be called up as auxiliaries.

Realistically, the cost of maintaining a large standing army is quite burdensome, so, unless the city is a fairly important border city (which it doesn't seem to be due to the fact that the walls are in such disrepair)