My Lady is in her eighth year of being diabetic. Since you are a diabetic yourself, I think you will find it very easy to manage.
Urine testing isn't very accurate, so I learned to check Lady's blood glucose myself with a human meter. It's very easy. I stick her inside her lip near her canine teeth.
I inject her in the scruff of the neck and rotate around in that area. Since the insulin needles are so small, I have never had a problem even after all these years.
Signs of low blood sugar in dogs are staggering, sleeping excessively, seizures, etc. Normal blood sugar is between 80-120 in dogs, but we usually don't like them to drop below 100 for safety. The target range is 100-200. I try to keep Lady under 175.
How long has this dog been diabetic? Do you know if he still has his vision? 90% of all diabetic dogs go blind within the first nine months. How quickly he was regulated and how well he has been maintained so far will determine the probably of him keeping his sight as cataracts from very early on when blood sugar is high.
Diabetic dogs have lots of eye problems including dry eye, uveitis, infections, lipids collecting behind the eye, ulcers, etc. Lady sees an opthamologist and still has her vision after all these years. She does have dry eye and gets drops and gels daily.
Diabetic dogs are also prone to uti's and other infections and they can be hard to clear up. I spend a lot of money on vet bills.
This is a great resource for those of us with diabetic dogs:
Pets with Diabetes: Home Page
I would suggest finding out as much as you can about how long this dog has been a diabetic and how well maintained he has been before adopting. Have the rescue get bloodwork done and fax it to your vet so you get an idea of organ function. If he has not been regulated and well taken care of, he could have organ damage. You want to know what you are getting into.