I can't access Amazon on this PC (dumb work machine policy), but it shouldn't be a problem. First, since the touch functions are infrared-based, it doesn't need the touch of a conductor like a capacitive touchscreen. So, breaking the IR plane through the plastic of the Ziploc should work just fine. Also, and this is the part I can't verify from the sites I've seen so far, it looks like there are hardware buttons on either side of the Kindle Touch.
Don't think there are. There is a brief mention that there is a way of turning a page other than "swiping" which for reading with one hand is useless. That to me is a deal breaker if I can't hold the Kindle touch in one hand and turn the pages it is pretty much a useless device.