Some diets you find online a very strict. I typically tell my patients no dairy, gluten, sugar or artificial sweeteners (technically even natural sweeteners can be an issue also), alcohol, peanuts, and dried fruit. Some practitioners tell their patients not to eat fruit, but I find this level of restriction makes it difficult to remain compliant.
DIAGNOSIS: ALWAYS based on symptoms. Blood tests aren't always positive and will tell you nothing about intestinal Candida overgrowth. There are companies that do more sophisticated stool testing for intestinal dysbiosis, but regular labs don't do this.
As far as probiotics, they are a must for treating Candida. Other treatment recommendations will vary with each patient.