Just a small UI suggestion. On the pop-up window that comes up when you do the operation "Split Stack" (either right-click menu or shift-click), in addition to the numeric entry field and the "Split" button, add 2 more buttons: "Split 5" and "Split 10" - because these are the among most common actions, especially when doing daily turn-ins.
(The other most common action is just splitting off one item, which you get naturally because the number field defaults to 1.)
I would guess that the above three choices - splitting 10, 5, and 1 item from the stack, makes up >95% of all split actions taken, and making available the above 2 buttons will save people tons of time, because they mostly don't have to futz around with the numeric entry field.