Hi dimensiondust, welcome to the guild.

Getting scale right is one of those hard problems in map-making. Designing a city or region that feels realistic takes a great deal of thought and experience but you're asking the right questions to get you started.

Here are some things that have really helped me as I've grappled with the same questions.
- Take a look at this resource, Medieval demographics made easy, this is a resource that I find invaluable for working out scale in maps. It's by no means exhaustive, but it's a great starting point for thinking about both regions and cities. For example, using this resource I would estimate the population of your town is 300-400.
- Look at real-world cities to help give you an idea of scale, Carcassone in France is a great one to look up on google maps as one of the largest surviving medieval walled cities.
- Depending on how deep you want to go, historical research will always help you out. Due to several modern inventions (cars etc) the size and layout of our modern cities is very different to what people built in a medieval context and this can steer you wrong when designing your cities (assuming you are designing medieval style or other historical style cities for your fantasy RPGs etc. I've been watching old episodes of Time Team (a British archaeology show) on youtube recently, and there are many other youtube channels that go deep on castle design, medieval industries and professions, medieval culture, etc. Having knowledge of all these areas really helps inform how you design your cities.