So a lil background on Hells Bells from wiki-answers.
what is the origin of the idiom hell's bells?-If you are unfortunate enough to get to, Hell, when you arrive there is a ceremony where new arrivals are required to ring bells, like church bells, to let all in Hell know you have arrived. In other words, Hell's bells, are what are rung to alert those that have been there a while, "You have company."
I know it contradicts my earlier theory but maybe Hells Bells do go off when we have outsider visitors?
On Stars and Stones, Something that struck me literally ten min ago as I reread changes. When Harry goes to the stone table there is very specifically 5 cold pure stars described as upon Lady nights throat(Hint hint!). I wonder if the phrase isn't connected to these stars and this stone table? conjecture, SNS will deal with how the table was made, how it works and why it can give power to a wellspring.
Chaos is depicted as an empty void.