Lots of information there.

I use a normal keyboard, plus some of my G15 keys.
Most of my stuff is done via keybind.

My mouse has two thumb buttons.
One is for my follow mapped key.
The other varies with the team.
And then I use the keybind approach.

As long as you know which button does what ability.
And can use them to react quickly, without thinking along the lines of "Which button is Flame Shock"...
Learning the devices, isn't really any different than learning keybinds.



Multiple presses of Tab will cycle through targets.
You could have one key to clear all Focus targets.
And another, for each Shammy to Focus the current target if they don't have a Focus, or otherwise cast Hex at their Focus if they do have a target.

Then you would cycle through the bad guys, having each Shammy assist the Pally and in turn press their Focus set key.
Possibly have a third button, which has all Shammies cast Hex at their Focus, should a Focus target exist.