So are you able to actually interrupt trade routes as a pirate ? Take their booty or demand payment to not take it and so on ?
Yes, from what I understand, the whole system is basically set up like this.
1. Continent 1 has a whole lot of X resources, but not Y resources. Continent 2 has a whole lot of Y resources, but not X resources. Carrying resources in a safe manner is inefficient due to inventory space. Instead, you want to convert resources to "packs" for bulk transport. When you have a Pack, you walk very, very slow unless you have a vehicle. A donkey is one vehicle, but cant cross water. A ship is another vehicle that can cross water and can carry tons of stuff.
2. So, the high level way to make money is to get a bunch of resources that are common in your region, load them on a big boat and head across the ocean to turn in your resources where they are most valuable. Its like playing the AH in WoW, except there is a catch. The ocean, like most high level zones, is open PvP. In addition to Pirates, the entire other faction can attack you. And the Pirates know the easiest ports from one continent to the other just as much as you do. An easier way to make money than collecting the X and Y resources, is to steal X and Y resources. If you sink a ship, or take control of it, you can unload the packs and put it in your ship, thereby taking all of the resources.
3. One of the problems of being a Pirate is that I don't think the first option to make money is available any more. You can't easily gather resources for transport because you dont have easy access to X or Y anymore (where before, you had easy access to 1 of them). So, to make mass money, you need to steal from others. One of the benefits of being a Pirate is that you have 2x the number of potential targets.
And straight up piracy is just part of the "infamy" system. Another aspect is stealing stuff. So, one of the ways to get X and Y resources is to grown them. You can plant stuff pretty much anywhere and then let it grow. There were people in my guild that never directly pirated because they didnt have enough people on, but instead just ran around to random islands and stuff and tried to find people that were running the equivalent of basement weed farms. You can protect your crops with a scarecrow, but that is relatively inefficient. For the mom and pops that are in high traffic areas, they all do it. But there are also risk takers who go to some random island for a few hours and try to grow a huge batch of something needed without any protection. They just rely on the fact that they are in the middle of no where and hope that no one comes along. Well, while your out sailing the seven seas, you can stop by the islands, see if you can find the lonely farmer and either take his stuff while he stands there powerless, you can kill him and then take his stuff, or you can even just tell him to pay you gold to leave him alone (which a lot of people will...at least in Korea).
So there are a lot of options if you want to be a straight "pirate playstyle," but here is my warning. On paper, it sounds pretty much perfect. In practice, there is a LOT of sailing around doing nothing. You might play 4 hours and not get anything. So it takes a special person / guild to want to do it full time. The standard "on demand, OMFG 6 min Queues" PvPer probably wont really find it fun. If you were the type of person that felt camping Pzyjn was fun, then you probably will do fine with being a Pirate. If you bitched because your guild mates were 8 min late for a pre-planned raid, then its probably not for you in practice, no matter how enticing it seems on paper.