a) Something similar to Command: Trigger actions by the area/screen the mouse is on could do that.
The SysInfo object can be used to find the current monitor resolution(s).
b) That would work. Another way, assuming you want the windows the same size across all the layouts for each case, might be to have a button that resizes the window to a fixed size. That can let you update layouts more easily.
It could even be used to save/update the current layout in two sizes, from a single button or hotkey. Although I think that would only work on the larger monitor (you can't resize something larger than all the screens).