u should have a banker and a guard then make a small small room (individual ones so mutiple people can keep their money) where u can put an iron door and a small chest and for every1 who open a bank account u give them a lever and put a sign at the top of the room to organized make sure u space out the rooms and have the guard escort them to thier room and the banker keep track of recordss

what iv built is a 9 coded door for the guards to open then im thinking about making a minecart system with a 3 coded lock for each player. but i dunno how to build it small .