Some hanseatic city sounds about right. The location does not seem to allow for more trading. You have access to to Icewind Dale (Furs?) and the Moonshae Island and thats about it. Waterdeep has the additional advantage of sitting at an estuary which allows easy access to Mithril Hall and Sliverymoon.
It would also match the political situation in that area with several allied big cities close together.
The really big trading city would probably be somewhere in the Sea of Fallen Stars as that one really serves as a shortcut to different parts of the world. If there were a channel in Okoth it would be huge.