There needs to be producers as well as merchants just as much as there are pirates. There also needs to be spoils for pirates to raid and an economy that allows traders to have the right economics to buy commodities low and to sell the spoils high. Silver and gold coins should be the currency of the era but you should be able to trade goods for other things. Stuff should require a lot of time and resources to produce products so they have great value and to are meaningful in the game . The name of the game should be trial and error to become wealthy either by starting off as a poor farmer who has bad weather precipitation or having a shop established with many contracts to suppliers that are very tricky to keep. Money should mean shame or respect and if not that life or death.