Here's your answers from someone you might know, including an avian vet:
http://www.the-chicken-chick.com/2012/05/diatomaceous-earth-de-benefitrisk.html
I was going to post the same link. I was going to use DE before reading it, now I'm not going to waste my money. I use the deep litter method, easier for me, better for our subzero winters and healthier for the chickens. And DE is not good for it, kills the good microbes and dries it out so it doesn't work. Chickenchick has a good article on deep litter even though she doesn't use it. It makes for healthier chicks also.
Worming chickens, I don't, my father never did his whole lifetime of having chickens and never had sick chickens. Lice and mites, I keep a pile of wood ashes in the corner of their coop for dustbaths, I can't say it works but I've never noticed any creepy crawlies on them.