Lucky you!....a dedicated room. I'm jealous.
I am definately an advocate of having nothing in between the speakers to affect the image and soundstage. And like Bryan said; a low rack and/or floor stands would be an alternative.
From the looks of your pictures, it appears as though you might have room for a traditional vertical rack on the 'left' wall between the wall shelves and the small window? Can't get a sense of scale much by viewing the pics on my computer screen

. That way you would still have ready access to the gear. Just a thought.
And as far as long speaker cables are concerned; if you're using solid state amps, 20 ft. or more shouldn't be an issue if the cables are 14 ga. or larger (soundwise, that is). Of course, if you choose an expensive boutique brand of wires, it could be costly...

Short term at least; I'd try your left-over granite slabs as floor stands until you're settled into the room. If it isn't to you're liking..you can always change it later on.
Good luck!
WEEZ