This is just a general rolling-in-dough money guide.
Send ships with a large capacity, preferably the East Indian ones with the 200 carry capacity, from these locations, carrying the following:
Liverpool to Campeche and Bordeaux to Natchez, both carrying guns. Then send the ships from Natchez to Liverpool, and the ships from Campeche to Bordeaux, carrying Fur and Sugar respectively.
Assuming a carry capacity of 200, with no loss to and from both destinations, you'll make a grand total of 426,400 for a round trip. I think that alone is enough to buy every single thing in the game.
The initial cost of the 8 ships and resources to fill them, assuming you start with no ships or resources, will be around the money required for the achievement, just for the record. But let's be honest, you really want that Pepperbox Pistol.