I think I own it but I am not sure.
It is another one of those highly confusing games where just because you buy something expencive it doesn't mean you are better off (in fact far from it...)
I think you'd know if you own it as it only recently came out (and is not out yet in some places. I think the steam version drops in 2 days)
As for buying, well you have to buy low and sell high. Right now I have a circuit of 4 cities which I have trade routes set up and move goods between them as the prices rise and fall. The economy is interesting, as cities specialize in goods. Lubeck produces a lot of salt but has no easily accessible game for meat. Aalborg has plenty of meat but needs salt to cure it. Malmo is the only city nearby which can produce wood and bricks in great supply, and is the only city currently producing cheese.
Among these three cities I have two ships running cargo and making a tidy profit.
Another system I like is that you cannot get to the advanced features without building your reputation and rank. Reputation is tracked per city; you gain reputation with a city when you bring in goods it is very short on and you lose reputation if you buy goods that are in short supply. You can only join a city's guild if your reputation is 25% or better and you've reached a certain rank as well.
Rank is determined by how you're doing. The first few ranks only require you to make money and increase your overall wealth. Buildings, ships, goods and cash all contribute to your wealth. After a certain point you must branch out and build some businesses as well to up your rank.