My preference is not to have the biopsy because at best they will be able to see inflammation of the upper layers of epidermis and you already know that.. if they pick up candida etc that is better tested from a stool test anyway, although if you are offered a colonoscopy I would take it. It is a relatively intrusive and uncomfortable test from what I hear. It involves placing a tube into the rectum and up through the digestive tract to see if there is any sign of disease.. this is what they do to see for sure if there is crohn's disease.. polyps on the intenstial lining of the wall etc, they will also be able to see candida overgrow with this test. The test is not nice but it does not leave a scar unlike the lip biopsy. Ideally the stool test is the best and just involves giving a stool sample, but modern doctors aren't really trained in health they are trained in disease, so in some cases these tests cannot be done unless privately through a nutritionist.
I know you have read good things about imuran on here but there's only been one major success from daniki and she has never returned to give an update. Very important that people who claim a cure update their situation every few months or years so that people know it works.. most people on here don't, sadly.
First things first, get all the diagnostic tests you can before taking any treatment. I know you are in a rush to get this problem sorted but you've got to be patient.
This is what I would do, you don't need to listen to me. If you want to do the imuran and the doctor's are monitoring you then it's an option to consider. I don't want to be negative because there's many different avenues you can take.