I cannot think of anything specific besides asking if there is any certain diet you should follow, what you will experience while on Metformin, and when would it be best for you to personally take Metformin (some doctors say different times, depends on the individual). I have also read about the vitamin deficiency and that is another good question to ask your doctor, although some doctors wait until a follow-up to see how you are doing on the medication, but ask anyways!
As for diet, this is my little plan, but everyone’s is different!
I eat mainly fruits, vegetables, whole grains, fish, chicken, and limit processed foods as much as possible along side limiting or avoiding eat meat completely.
Posting this as a question for others to answer as well, and people can also send in an ask since the limit is so short! I hope this helps!