Pipe freeze question… help

To prepare for tomorrow's low temperatures I decided to turn of the main water line and drain the pipes just by keeping the faucets open. My attic hot and cold pipes are not insulated. Due to being very oddly placed i am not able to so them myself. I have a gas boiler 40 gallon in the attic. I just read online and not sure if it's true or not that i shouldn't keep my gas boiler running when water supply is off, it can damage the heating elements or even cause fire. Is that true, should I turn of my gas boiler?

Also, was it a bad idea to turn of main water line and drain the pipes? Should I just have relied on dripping the faucets?