In reading your post, it looks like you have just been on this new eating plan for 10 days. Is that correct?
Most of us on Connect are not trained to answer the questions you have posted. You might want to consult with a dietician to have an explanation for all of your questions. Appointments with dieticians are not always covered by insurance, however, it might be worth the expenditure of money for one appointment. If that is not an option you might see if your GI doctor has an RN or a PA who might be willing to talk with you about the reasons for the restrictions of the food plan you mentioned. Then again, you might just need to try this food plan and accept the fact that while it may not make you happy (eliminating foods you really enjoy), it might be worth a try to see if your symptoms improve.
Also, please remember that you can always seek a second opinion if you feel that you are not getting the results that you need.
I hope that you are successful in making this adjustment and in getting answers to your questions.