I truly believe that 'bank account' should be linked to 'trading system'. In other words, if we have a trading system (which a lot of us have been waiting for), trading money should be a one of the items that can be traded. I do not personally agree with a third party bank as in real life. In real life there is FDIC that acts as an agent to guarantee bank customer's money from missing because of no-fault of the banking system (in case of major natural disaster, for instance). In Potco, who is going to guarantee that any player on the 'banking system' would be honest enough to perform this job (referring to D-Rock's idea about guild internal finance system)?
Since there is no agent that could fall into the category of warrantor, there is no agent that could be worthy of overseeing financial transaction in Potco. So in my opinion, money trading should be left into individual pirate's hand. If there are two pirates who want to give away and receive gold, let them deal with it. So I'm going to the opposite direction of D-Rock's idea, a guild cannot boast over how much gold it has.
I have mentioned long ago on one of the threads about Trading system, that 'gift' - as one of the forms of trading - should be able to be designed by Potco game designers earlier than any other form of trading. It was mentioned also in that thread, that there should be several forms of trading. But the other forms of trading - other than 'gift' - do not look as easy to design as 'gift' (auction, bid, etc.). Gift only involves two parties; the giver and the receiver.
The transaction could be executed as follows. We should have a communication window such as a 'button' on our pirate card. When we click a friend's pirate card, we should be able to see a 'gift' button, and when we click that button, there should pop up a window of our treasure/inventory chest. Then we could click 'gold' (or any weapon/clothing/and any item there), then there should come up another communication window about how much gold we'd like to give away. After we type the number, it should be confirmed by another window, saying, "Are you sure you want to give away this gold to your pirate friend?" with YES/NO button. If we click 'yes', it means that a certain amount of gold will be transfered to our pirate friend, whose pirate card we click to begin this transaction. As simple as that.
As for in-game rewards for guild members, it sounds good to give incentives to the guild members. It sounds like other MMORPG games where a guild is like an 'organization'. It has its own guild money and inventory, where the Guildmaster and Officers would be the managers of guild capitals, and members of the guild are required to pay dues to the guild. But unless Disney Potco is ready to move this entire game into that direction, I think it's too far fetch. Gold has to be treated the same as any other item/property (weapon, clothing, jewels, treasures, etc.); gold is just one item in the entire inventory. If we could transfer gold, we should be able to transfer any other item/property.