That's a difficult question to answer, as for part of the 17th century Zeeuws Vlaanderen was a war zone. In theory people would go to Antwerpen, Brugge or Gent. In reality, no. Because of the 80 years war. Travelling to Middelburg was more likely, but much more difficult, as they had to cross the Westerschelde. Travelling further, to Rotterdam or Amsterdam ...
You can get some information concerning the number of markets relative to population by looking at the Wikipedia page on Market Towns. One specific tidbit there might be of use to you (emphasis mine).
The primary purpose of a market town is the provision of goods and
services to the surrounding locality.1 Although market towns were
known in antiquity, their ...
It's a bit late in the period, but this 1572 map of Antwerp, with a population that year of about 125,000 lists at least 5 markets in the legend:
Die Grote Marct. - The Big Market.
Centre, just north of the main church
Die Ossemarct. - The Ox Market.
Just inside the East Wall, between the two main gates
Die Peerdemar[ct] - The Horse[?] Market.
One block ...