So during a cold crash I sucked around a quart of StarSan onto my beer, there's a layer ~1/2 inch thick sitting on top of the beer. Should I try to siphon off this top layer, or wait until i get a keg (a week or two) and just rack whats underneath it?
Don't worry too much about it. As @valverij said, StarSan is safe to drink at this concentration. I would try to siphon most of it off, especially if you need to move the beer before kegging. Moving it will likely mix the beer with the sanitizer.
StarSan in water is almost without any smell or taste, so I don't think it will affect your beer much even if you leave it in.
No worries, BUT: take your beer out of cold conditioning and let it warm up to diecetyl rest temperature. You will see some action in your airlock as the yeast consume the chemicals that are in star san. Wait until activity has finished and then cold crash again with out adding more star san! :P
I recommend using a bubbler when cold crashing as the liquid will not be sucked into your beer. Otherwise, put a loose knot in your blow-off tube, this can create the same effect as a bubbler.
Like the other answers, don't worry too much. You don't want it in your beer though, it will add a sour hint of acid.
It would seem you could siphon off the top but you cant, it mixes too easily. Trick is to rack the beer "out" of the trub on the bottom and the starsan on top.
Next time do slow temp drops 1° an hour. Idea is to allow co2 production to compensate for gas shrinkage. Or cap the fermentor with a starter sponge or foil.