Thanks, but I think an amateur like me (despite playing this game on and off for ten years) will stick with what I know. I actually do very little trading apart from the fairly early years because by the time I've researched all the things you mention, everybody else has already declared war on me, whether I want it or not, and my caravans get zapped before they get to their destinations.
I build Adam Smiths Trading Post then all my buildings costing 1 maintenance will be free and I just build a few buildings costing more than 1 where I need them.