With requiecast + HS macro you dont miss the fifth HS hit enchanced by the buff. It doesnt matter if your HS will deal damage after the buff is gone, damage is increased at the time you press the button. If you would press HS 1 sec before the buff will wear off and your character will cast the spell after the buff is finished, you still will get the bonus damage boost for that spell. I have just tested it, I had never miss the bonus for fifth spell with my macro.
About those cd's.
I dont have holy ground in macro i do not recommend anyone to put it there, it always should be separate. Deffensive cooldown whichever you will use they are good enough to keep you alive, i dont think people actually think which one def CD should they use, having it in one button at least guarantees you that you will never forget about the CD and you will use every one available instead of traveling across the button thinking which one should you use, you just press one button and here you go, little to no place for mistakes here. In raids you could predict when to use them, you dont have to be on deff cd's all the time. One button with all the cd's takes very little attention, which allows you to pay more focus on the stuff happening around you instead of thinking how to press X or Y or which should you press.
As for mixing oGCD skills with the GCD, i dont see any problems here. Pressing macro with oGCD first and GCD second will work exactly the same as you would use them on two separate buttons. You still have to wait for part of the animation to go through with any skill you use, i believe its something between 0.2-0.25 sec of delay between oGCD and GCD skills. Making a macro of them could potentially affect your dps and raise it up, since you dont waste time to travel across buttons so much, it prevents you from forgetting to use oGCD which will have significant impact on your performance.
And secondly, that sword/shield macro works perfectly fine, each press of the button will switch you from one to another. Its just that you cant turn off the stance like you would do with a separate button, but who would want to turn the stance off anyway, at least you will never turn off the stance by a mistake that way.
Btw i dont see the place for gauge limit on your hotbar, this thing could be useful a ton when playing trials and failed to do some mechanics.