I did the *exact* same thing last month. Dropped 100lbs unrinsed Old Castle Sand into my 90gal tank on top of my live rock and had alot of the same concerns. The cloud took just over a week to die down the first time, but now even when I stir it up moving things it calms down pretty quickly. I'm told this is due to bacteria colonizing the grains of sand and making them heavier (?).
The foam also went away in a week or so. I would not personally worry about it harming your live rock. In the wild, figure that the rock gets swamped occasionally by sandstorms now and then. Once the initial cloud clears you can go in with a (new, unused) turkey baster and blast the small bits of sand off your rock.
I will say that after all is said and done I am very happy with my old castle sand. It turned from that original drab brown color to a nice white, and gives my tank a very natural look.
Keep the powerheads going, and maybe towards the end run some GAC
if you like.
Hang in there.