You need to figure out what kind of mites they are, in order to properly eradicate them. Here is an infographic which explains it better - http://www.poultrydvm.com/featured-infographic/identifying-common-ectoparasites-of-backyard-poultry
The biggest thing with bumblefoot is modifying the environment. Such as keeping it clean, using a different substrate, keeping their area dry, etc. Here is more info about it - http://www.poultrydvm.com/condition/bumblefoot
Here is an infographic about helping you figure out which bugs are bothering your birds - http://www.poultrydvm.com/featured-infographic/identifying-common-ectoparasites-of-backyard-poultry perhaps this might be beneficial for you.
You aren't nuts, you are smart. I would recommend predator proofing the top and putting something that isn't going to collapse if snow falls on top of it. Therefore, you'll probably have to add some support columns and slope it somewhat so the snow slides off. Here is a good infographic on...
Oh no that's awful :( I am so sorry. I think it sorta depends on your setup as to what possible predators could have gotten inside and eaten all the birds that quickly. You may want to think about predator proofing your pen to prevent it from happening again....here are some good tips on how to...
If it were me, I would do what I could to keep the snake from getting in. Have you tried different tactics to get rid of it? Here is an infographic with some good tips - http://www.poultrydvm.com/featured-infographic/dealing-with-ratsnakes-in-chicken-coops
It sorta looks like his feet are a bit puffy. The first thing that crossed my mind was gout.....here is some info about it, it is more common then people realize in chickens - http://www.poultrydvm.com/condition/gout