Yes, low FODMAP isn't something you'd want to do permanently, it's more of a way to get a break from sympoms of GI distress. Of course, and CD will say this if he sees your question, water fasting and juicing are the fastest and most effective way to do the same thing.

I was just reading an article on these exact issues and questions, I'll find it and link it.

As far as fats go, you're ultimately going to need cholesterol for testosterone and every other hormone. They certainly shouldn't present any digestive issues for a healthy gut, which water fasting and juice feasting for long periods help create. I'm no expert, but I will say, if nothing else, be careful with coconut oil for awhile if you have serious dysbiosis. It's antifungal properties can cause die-off just like any other probiotic.

Unfortunately, the best and only thing you can ultimately do is slowly, carefully experiment with your own system, research every day, draw connections, and, #1 in importance, listen to your body/intuition. Let me find that article.