First, I'm sorry you're having all these issues. They sound like reasonable requests, and I'm sure they're all possible.
I'd love to help, but there's a lot here, and a lot of questions to ask and things to try. It's more than I can really offer through the forums, for one, because it's just not practical, and two, because it takes a lot of my time, which, as a developer yourself, you probably know has value.
I'm not sure what your situation is, but if you have a budget to work with, we could make a lot of progress by commissioning the support work from me. If you'd like to do that, contact me through my website and we can talk details.