But lategame - at least for me - turned out to be REALLY boring. (the whole 'buy the prince's land' mission line is soul crashingly repetitive.)
The people usually did two hubs because of a technical reason: on professional difficulty the harbors can freeze in the winter.
To overcome this they used more than 1 hub (otherwise your whole system would get stuck if and when the central hub freezes).
Be aware though, that balancing stockpiles around 2, 3 and more hubs quickly becomes a nightmare.
First I'd build only 1. If you are really into two, then pick two towns based purely on sailing distances. Aka pick the first town which can cover the eastern part (baltics, and the denmark cross) then pirck the second which is central to the western part (lowlands, england, and the western part of norway, etc.).
You can also lurk around these forums and find savegames (I remember vividly that I was able to find a working save, although it modified the map files so I had to overwrite ssome game files for it to work though).
Sorry for the late and probably opaque answer!