I will qualify this as a sort of Non-Answer, but more of a guideline.
Follow Maslow's Hierarch of needs as a model, and couple it with specialization.
As has been stated, most communities are likely to have a blacksmith or farrier and a bunch of farmers. Call it 50 folks per town. I would say that around that time you will get an Inn, based on proximity to a road or navigable waterway. Flowing water will bring a mill. I suspect his might happen around 75 people.
Now we get to Maslows Heirarchy. The above is a guess at what point further specialization to begin. The first thing that individuals, and by extension the community, wants is to provide for the physiological. Food, Shelter, Etc. By the time you get specialization and the purely physical necessities are met and exceeded, maybe at 75 people, you can get further specialization with additional craftsmen. Carpenters, Wainwrights, Pottery makers, and so on. This represents the security phase. YOu have enough, it's time to make sure this state of affairs continues. You are now in a position to sell the surplus, but if you are selling, you need people to buy. You have to attract them by making sure there is more that one way to get to the inn. Waterways, build roads to other places maybe. That might be at around 150 people. As the town grows, opportunites for further specialization is going to come up. If you assume one blacksmith per 50 people, at 150 people you might get a blacksmith AND a farrier AND a weaponsmith. That takes care of tools and Horseshoes and sharp things. Take some of the apprentice metalsmiths and then you might get a silversmith out of the bunch. This launches you into civic pride, or the Love and Belonging phase.
Just remember that every specialization adds to surplus and will have a purpose based on location and local natural resources. Lots of iron might mean additional weaponsmiths. Fertile ground might mean an agricultural hub. Esay transport might give you means to start a Bazaar.
Just use a little logic.