**my opinion, I'm not a medical professional**
You are absolutely right...there are tons of people out there living with various degrees and levels of these diseases. And everyone is affected differently so it's hard to find answers. The thing is, there is no miracle cure, but with a lot of hard work things can get much much better. It sounds like Dr. Mackalski is someone your husband should definitely try to get to see, because I would say that he needs a formal diagnosis and will likely need medication to get out of the spot that he is in (sounds like he has the most severe symptoms).
In the meantime, are you on facebook? If so, join this page
https://www.facebook.com/groups/254381904904394/ for tons of support and thousands of personal accounts and advice from others going through a similar experience. Spend some time scrolling down through the page.
As others have said, he should definitely avoid all dairy, grains, caffeine, soda, spices etc for now. Limit fruit and make sure it's quite ripe. Veggies should be very well cooked, to the point of mushy. You can liquefy this in a blender if needed. Ground meat is easier to digest for now. Don't try any probiotics just yet, but that will definitely be a help to him in the future. Good Luck to you and your husband!!