Haha, you sound like me when my man calls me a "worried chicken mama"
I think the poo page that was linked is a good resource. I usually give my girls some scrambled eggs every now and then as well. If you make sure they are totally cooked, not runny at all, it gives them some much needed protein and from what I've read won't lead to egg eating since cooked eggs taste different than raw (and they aren't in the shell). The extra protein helps keep down feather pecking too.
Chickens LOVE grass and weeds! Whenever you think they are doing something weird, just imagine how people kept chickens 150 years ago. They walked around the house all day, pecking at any grains, bugs, weeds, or plants that grew. They had humans who stayed near the house all day and dogs to protect them. Anything they would do normally then, should be good for them now.
My personal opinion on vaccination, based solely on what I've read in books and here on the forums, is that it's not worth it unless done while they are chicks. Coccidiosis mostly affects chicks, and Mareks vaccines are a pain to administer and can potentially give your chickens the disease instead of innoculating them against it. If I ever get adult birds (rather than chicks) to add to the flock I might change my tune, but since I don't plan on adding more chickens from untrustworthy sources I don't think it is worth the risk at this point.
DE is the best stuff ever. I just sprinkle it on any nice fresh poops that the flies are congregating around, and they quickly disperse. Some people mix it in with the litter inside the coop as well, but since I'm using SweetPDZ it's too dry for flies in there. If you put some in their favourite dust bathing spots, it will help kill any nasties crawling around on them, and if you mix it in with their food (I forgot the ratio, I usually just kind of toss a handful in every now and then) it will get rid of internal parasites as well. Bonus - if you have ants in your house, you can sprinkle it around the baseboards to keep them out! DE is the real-life Windex