"Left click on combined items" to "open list"

Like this.

And choose how many are opened before combining

That's possible with 7+ Taskbar Numberer. See here:

https://superuser.com/a/916838

Thanks, can the number be shown beside the icon like the picture above?

What about left click for list and middle click for thumbnail previews?

Currently that's not possible with 7+ Taskbar Tweaker. I tried to implement this once, but it turned out clumsy and confusing.