You should look more in the ReadMe :P
I have written it, but i know my english and explanations aren't the best.

Just some hints:
I cannot find a way to set the task background image
http://www.xdocs.ls-universe.info/pie.php?xTaskbar2#TextureSettings

For some Tooltip Modifications:
xTaskbarTooltipMode METHOD
METHOD can be one of the following:
".prefix-caption-file" -> Default
".caption-file"
".prefix-caption"
".caption"
".prefix-file"
".file"

Try xTaskbarAutoSize for your Taskbar:
AutoSize MaxTaskbarSIZE(int) [STEPS(int)] [DELAY(int)]
The Taskbar resizes/repositions itself according to the settings!
You must additionally set:

xTaskbarButtonMaxWidth
xTaskbarButtonMaxHeight

MaxTaskbarSIZE is either the maximum Width (Layout .horizontal) or Height (Layout .vertical) of the Taskbar.

Maybe it helps, at least all you want is possible somehow.