For the bank you should make it so you lose 2.5% of your gralats when you did (for instance you would lose 25 gralats if you had 1000 and died). Then make it cost money to start a bank account and extra for more storage and a bank card. There could also been a 5 gralat fee for depositing and withdrawing and donating. You could donate to your friends if you had a bank card by finding them in your friends list and pressing the more actions button and then tapping on donate which lets you set a certain amount to donate. For all transaction you need to be depositing a least 25g or withdrawing at least 25g (same with donations). For a bank account a starter should be 1000g and hold 25,000g, a premium bank account should cost 2500g and hold 500,000g and an elite account should cost 1000g and hold unlimited gralats. A bank card will be 5000g and let you donate, gain interest (interest is 0.5% per day on a starter acc, 2.5% on a premium and 10% on an elite), deposit gralats at any bank branch and take out loans (5% interest per day on loans and it automatically pays back the bank when you gain money, also you get your bank account removed and your furniture taken of you don't pay back for six months). The amount you could take out on loans would depend on your account, starter would be 1000g, premium would be 5000g and elite would be 25,000g.
Also another idea is that I think you should be able to sell your items at market which opens three times a day for two hours. On weekends markets run all day. You can rent a stall for 500g and sell as much as you want for 15 mins. The prices on your items can be as high as you want.