I'm not sure kombucha is the best thing for diabetes. I was making it, but then I stopped when I came into the pre-diabetes range. I haven't been back in it since I stopped kombucha. Some experts like Sandor Katz have expressed some concerns about kombucha with diabetes. Kombucha is super easy to make. The more appropriate question is to ask-is it a good idea for you?
I read a lot about "black seed" as helping diabetics reverse their blood sugar issues. have you done any research on that? I was also starting to become prediabetic before overhauling my diet to a Weston A price type diet. That was 2 yrs ago and no problems in that department thus far. I would probably wait on the kombucha, you may have to ferment it so long that it wouldn't even taste good.
Companion Planting Guide by World Permaculture Association