First the main window cannot be given the +Resize option, or it's contents will drift off the window diagonally down and to the right. I think this is related to the third question.
Second, the scrolling with the mouse will only work at first launch. Once you click anywhere in the window it no longer works until you restart the script. Is there a way to scroll the window panel that is underneath the mouse?
Thirdly, it does not consider the size of the child windows as part of the scroll bar height or width calculation. Does anyone know of a way to add the child windows to the calculation?
Here is the code taken from Lexikos' example https://autohotkey.com/board/topic/26033-scrollable-gui-proof-of-concept/#entry168174
Something Like This: