I have a few foster Kitties that I took in and they never left me. One has just been diagnosed with Diabetes. I am very happy to have found this group and look forward to some direction.
Welcome to FDMB, the best place you never wanted to be!
What insulin will or are you using? The 4 which last about 12 hours per shot are Levemir, ProZinc, BCP PZI, and Lantus. Other insulins tend not to last a full 12 hours, leaving the glucose uncontrolled unless you give it every 8 hours. This can be difficult for many folk's schedules.
Are you already using insulin? If so, your first task is learning to home test the blood glucose, to keep your cat safe. You'll need an inexpensive glucometer such as the WalMart Confirm or the Target Up and Up, matching test strips, and lancets for alternate site testing (25-28 gauge).
If not, then you'll want to look at low carb, over the counter foods which will help reduce the workload on the pancreas. Cat Info explains why you should do this. In general, almost no dry foods in the US are low carb, plus cats evolved to get their water from what they eat, so they tend not to drink enough when eating dry food. I feed all 15 in my place Friskies pates, which has 13 oz cans.