I just looked up some medieval demographics to get a sense of scale, and I think it'll be safe to make an estimate like...
Big cities/capitals (Ketra, Arca, Reajh) have a population of like 100,000+ people. I think those cities are the sort where you could wander for days and get lost. xD
Smaller cities (Cerenis, Selevea) probably around 8,000 - 12,000+. I think La'marri and Zantaric would fall more in that range.
These are just some ideas off the top of my head! I'd have to give it more thought, but those are some starting numbers to work with. 8D So capitols = BIIIG. XD Like the New Yorks of their time!