Here's a great start: https://www.nutriliving.com/blog/im-prediabetic-what-do-i-do-now
You can also check out the recommendations we have for diabetics:
Regarding your other questions. I suggest you get with a personal RD in your area so she can get a good overall view of your health history and provide specific recommendations on supplements and foods for any nutrient deficiencies. You can find one in your area (one that even specializes in diabetes) from this link here: http://www.eatright.org/find-an-expert
Vitamin D and B12 are in mostly animal-based foods or fortified foods. He/she may suggest vitamin supplements.