Generally, we noticed that the guards tend to follow a predictable patrol route, allowing us to easily take the same route back and forth between the vault and the escape with little issue. Our general plan was to find the security room, kill both guards in safe area, find the computer with someone still in casing mode, try and activate without alerting civs (and ecm/tieing them up/breaking cameras if it went bad), wait for new cops, move into back room to stealth open the vault (while avoiding guards). (With the addition of the new fugitive skill to pick up items in casing mode, the extra keycard is even more valuable as it allows us to guarantee being able to open the server room without risking being spotted by any civillians.)
(silent, doesn't involve treking back through the bank)
This is a bit off the top of my head, but when I did stealth with my crew we used: