I had a dog with Cushings. I gave her Drenamin (by Standard Process --- I ordered mine from spinelife.com -- was cheapest at the time and their shipping is pretty quick). It is bovine adrenal extract (and others). I also gave her milk thistle for liver support (cushings bad on liver), colostrum for immune support (cushings is auto-immune disorder), probiotics, and digestive enzymes. There was more stuff, but she was also diabetic and had hypothyroidism.
THe enzymes that made such a HUGE difference in her were called Vet-Zimes Formula V4. Not sure if there was anything special about them or not, but they worked great so I continued. THe vet has to order them, though. A vet had given them to me not long after Chewey's diagnosis. I gave her the bottle. He had given me other things, too. With the costs of everything, I didn't think they were necessary, so I quit giving them to her when the bottle was finished. The next day she started acting like she felt terrible again. It took me a few days to piece it together. As soon as I figured it out, I ran to the vet. She perked up soon after I gave it to her again.
I could only do this line of treatment for a couple years before it all got too bad. If the cushings is not controlled, it is impossible to control insulin levels. At the time Trilostane was not very common and had to be imported from England. I had initially shied away from drugs because of the side effects (like chemo). Trilostane was not supposed to have those side effects. My vet had never even heard of it but we ordered it anyhow. She was shocked at the great results (with absolutely no side effects). You just have to get tests done frequently, as with any medicinal treatment.
I made Chewey's food. It was basically meat and vegetables. Luckily, she absolutely loved vegetables.
If you haven't read it yet and are new to Cushings, the book Dogs, Diet, and Disease (or something like that) is very helpful.
Not sure if you vaccinate or not, but if you do, stop immediately. Your dog's immune system cannot handle vaccines. Also, think about stopping heartworm pills if you give them. Just read into it and think about it.