I send my merchants in batches of 3. Oh, I fully acknowledge the 'empty slot' method is superior, but I get a little thrill out of pushing some merchant out of business and it saves a lot of searching for an open CoT.
Trading is DEFINITELY worth it, and the micromanaging isn't really so bad once you get used to it. In the latest betas and 1.09 the AI's a lot less likely to embargo you, so I blitz a CoT all at once, then just sit back and see where it resettles. Again, almost certainly not ideal, but I amuse easily and it works.
As a European trading early isn't recommended unless you're Venice or Genoa. Too many little minors, and your trading efficiency's too poor. Wait til the world stabilizes a little. By Trade-3 you should be ready to go.
The AI DOES merchant spam when you load the game, so don't be surprised to take some serious hits. That's okay - take your slots back.
That's all I can think of at the moment. Don't do many (if ANY) Trade Agreements nor Trade Embargos. It messes up your Trade efficiency, which affects how much money you get and how easy it is to knock you out of your slot.