1, 2, & 3 are what I'm planning on using, since I started before hotbars could be reshaped.  
4, 5, & 6 are the same thing reformatted to match the 3x4 grid of MMO mice.

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Hotbars 3/4 are unmodified and have the buttons you'll be hitting the most (single target + follow-ups)

Hotbars 1/6 are Shift modified and have your next most frequent buttons for less pinky strain (AoE + situational utility, macro is your dex potion)

Hotbars 2/5 are Control modified and have the *really* situational utilities. If I was starting fresh, I'd move some of them around, but muscle memory is a prison.

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Three Slithers are included since there's so much open space.  
Ctrl+6: Unmodified - dash to current target (boss)  
Ctrl+3: Macro (/ac "Slither <f>) to dash to your focus target - handy to always go to your assigned buddy for stack-ups and such.  
Ctrl+4: Macro (/ac "Slither" <mo>)  to dash to whoever/whatever you hover your mouse over.

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Each group of 3 buttons across modifiers are logistically connected, at least loosely.

1 & 3 are your normal filler rotation with the AoE version on Shift.  
1 (left side) sets you up for Flank positionals.  
3 (right side) sets you up for Rear positionals.  
2 is your Rattle spender and your Rattle granter on Shift. The jump from 2 to 11 for Reawaken might be a bit much, but I have a feeling the opener will have you do other things between those presses.

4, 5, & 6 are your follow-up abilities with important utilities on Shift and Control. This row is basically the middle of the thumbpad, so it's an easy spot for me to quickly hit for those oGCDs, dashes, etc.

7, 8, & 9 are the Twinblade attacks, again with AoE on Shift.  
7 (left side) is your Flank positional.  
9 (right side) is your Rear positional.  
Sample order for setting up Recast Speed first would be:  
8->9->(6->4)->7->(4->6)  
Which is a nice looping motion.

10, 11, & 12 (aka 0, -, &=) are entirely utility, plus Reawaken.
Reawaken/Generation/Legacy/Oroboros order goes:  
11->1->(5)->3->(5)->7->(5)->9->(5)->11  
Which is kinda like drawing a X/Z sigil with your thumb. I'll admit, the jump from 5 to 11 is not great, especially with weaving an oGCD into a ~2 sec recast. Putting Reawaken on Ctrl+2 or Ctrl+8 might be a good idea to reduce strain.  
EDIT: Moved a Slither to Ctrl+3 to make room for a second Reawaken on Ctrl+5 for reduced thumb travel.

julianne_hardstone