A great quick-start! Everyone might want to change something for their opinion of how - but its great to see an initial "just use these numbers" and why. Reminds me a bit of rolling up a subsector in Traveller - and maybe a similar methodology could be used here. Also, remember that trade roads follow waterways and military roads cross them at right angles for fording. When those intersect, you get towns with ferries, support services which build up from supporting camps as large groups stage and cross rivers or lakes.