I just discovered that, coincidentally, WIN+TAB and WIN+SHIFT+TAB already do part of what I was asking for. It does cycle through the taskbar buttons in the order they appear. However, there are two problems (for me) with the way it works:
1/ When you release WIN+TAB, it does not automatically restore the window of the selected button.
2/ Every time you press WIN+TAB to begin cycling, it always starts at the same button. I would like the first WIN+TAB to begin with the task button immediately to the right of the currently selected button (if any). Similarly, WIN+SHIFT+TAB should begin with the task button immediately to the left.
Anyone care to address these?