Yep, that's totally possible! 

- You'll need to include an extra section of dialogue after selecting an item, where the player is asked a quantity for their deposit. Make a new variable for each slot for the quantity of each item, and use the Input Number to store the player's desired quantity to the relevant variable. 

- Make a Conditional Branch that checks if the player is carrying the same amount or more of the number they put in. If they don't, return all the slot variables to zero. But if they do, you can keep the Input variable as it is. Make sure to remove the quantity of items from the player's inventory.

- When it comes to withdrawing the items, make sure to return the quantity in the variable to the player's inventory. Be mindful if your game has an item limit (the default is 99) that the player doesn't receive too many and some of the withdrawal gets wasted. You can get around that by creating another variable that checks how many items the player has, and compare it against the bank slot quantity.

- There is a script call to work out how many items the player is carrying if that helps too. You should be able to use $gameParty.numItems(1) to find the quantity of item ID 1 the player is carrying. You can also use variables inside that script call, so try $gameParty.numItems($dataItems[$gameVariables.value(1)]) to find the quantity of items under the item ID stored in variable 1.

I hope that makes sense! :D