Now this volcanic city is not just any volcanic island, it is only a couple hundred miles above the northernmost tropic but that really isn't important, what is important is that the coasts of the island approximates a triangle very closely. So if your following along on paper you should draw a triangle pointing downwards to represent the island, however at the bottom you see it compared to crete so you don't need to.
on each coast (especially the west and north) there is volcanic mountains, this should make especially fertile soil from what I know. So on the northeast corner of the island there is a massive city, it has access to a bay and the vast majority of rivers/creeks run into it, it is the only major city on the island so how big could it get?
For further detail, the island is not physically isolated, however the inhabitants are very isolationist believing that the surrounding lands are ruled by a demon out to destroy them. However eventually the island was invaded and the invasion was not beaten back and the inhabitants realized that the neighboring land wasn't controlled by a Demon and so they began trading with the land to their west. The east coast cannot see any land east of them (except maybe a few islets). The question is really how big this port city would be and if it would be reasonable for their to be a port city before they began their trade with the west?
The inhabitants have wings but (from what I know) can only glide, if it would be more reasonable for the city to be inland (maybe in the islands middle) then a port the question of how big a city this island can support still remains the same.
they have iron but saying that they are bronze age or midevil level technology would be... not the best descriptor. They can work metal, they have farming technology specialized to maximize their food production with simple tools and no major domesticable animals.