I voted "mostly a good idea" because I think "city" level is slightly too concentrated. I'd divide it into 4 channels:
Odus, West Antonica, East Antonica, and Faydwer.
While it is essentially continent wide, the E/W Antonica division takes care of the Qeynos-Freeport dilemma. Faydwer and Odus are so small that I don't think it's problematic to run 5 - 10 minutes to make a sale. If you place yourself in an obscure location, you should be expecting at least some amount of travel to make it to the logical point of trade.
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