Thanks for the information above.

I guess everybody agrees that the shortcut to richness is the four western trade nodes. It does not even require any knowledge on trading mechanics and strategy to make lots of money and stay rich in the campaign. Of course, figureing out the mechanics and details is fun, but it probably will not change any strategic decision that the player needs to make. (1) Fill the nodes with 10 trade ships; (2) Make as many trade partners are you can.

But maybe we can have a more in-depth look at how much money exactly we can expect from each trade node, and compare that with incomes we can expect from tax, etc. But I would bet on "shipping a stack to northern Kyushu as early as possible".