- An endless number of widgets in a column: Sounds like a GtkVBox.
- Vertical scrollbar: Put your VBox in a GtkScrolledWindow.
- Horizontal stretching: This requires setting the appropriate properties for the VBox, ScrolledWindow, and your other widgets. At least in Glade the defaults seem to mostly handle this (You will probably want to change the scrollbar policy of the ScrolledWindow).
Now for the trick. If you just do what I've listed above, the contents of the VBox will try to resize vertically as well as horizontally, and you won't get your scrollbar. The solution is to place your VBox in a GtkViewport.
So the final hierarchy is ScrolledWindow( Viewport( VBox( widgets ) ) ).